There are many theories if age affects second language acquisition. Some authors saying that, to learn a second language when you are child is easier than to learn a second language when you are older. We can define children ages from 3 to 18 that are in school and adults or older learners from the ages of 18 and above. However the critical period hypothesis it can also play a role in the learning and also the implicit and the explicit shift hypothesis. Below will examine what authors point out. What is the difference of learning a second language in early stage or later, the benefits and the negatives. And when is easier to start learning a second language.
To start with, in critical period hypothesis suggests that there is a period when language acquisition takes place naturally and effortlessly. Penfield and Roberts (1959 in Ellis, 1985:107) argued that the optimum age for language acquisition it starts the first ten years of life. Because in this time of period the brain retains plasticity but with the onset of puberty this plasticity begins to disappear. They suggest that this is a result of the lateralization of the language function in the left hemispheres of the brain, and slowly concentrated in the left hemisphere for most people. Thus, increased difficulty which learners supposedly experience as a direct result of a neurological change.
According to Lenneberg (1967 in Ellis, 1985:107) to support the critical period hypothesis found that injuries to the right hemisphere caused more language problems in children than in adults. He also found that in cases of children who underwent surgery of the left hemisphere, no speech disorders resulted, whereas with adults almost total language occurred. Furthermore, Lenneberg provided evidence to show that whereas children rapidly recovered total language control after such operations, adults did not do so, but instead continued to display permanent linguistic impairment. This suggested that the neurological basis of language in children and adults was different. However, Lenneberg's evidence does not demonstrate that is easier to acquire language before puberty but he assumed that language acquisition was easier to children. According to Lightbown and Spada (1999:61) most studies of the relationship between age of acquisition and second language development have focused on learners' phonological (pronunciation) achievement. In general, these studies have concluded that older learners almost inevitably have a noticeable 'foreign accent'.
However, another interesting cognitive theory is the implicit and the explicit shift. This suggests that the age affects the decreasing in language learning capacity in SLA and it happens because of the declining role of implicit learning and memory in the language acquisition process, and at the same time increase the role of explicit learning and memory. This statement is supported by a wide agreement that learners process their late-learnt language differently than their native language, but the results of the performance are rarely the same. Paradis (2004 in Dornyei 2009:256-257) point out that a particular strength of the implicit and the explicit shift hypothesis is that they can account of the age effects in naturalistic SLA and in formal school learning: first, the dominating learning mechanism is the implicit thus the younger we are, the better we can capitalize. Second the limited amount of L2 exposure and cognitive structure input is typically favours explicit learning and learning we can benefit from this language environment more in older age when the implicit and the explicit shift is on the way and thus prepared us for utilizing explicit learning mechanisms. Although it is often assumed that the loss of the implicit learning that is forces the second language learners to rely in the explicit learning, which uses a cognitive system different from that the native language is support.
Dekeyser (2000 in Dornyei, 2009:241) point out that if the Critical Period Hypothesis (CPH) is constrained, however in the implicit learning mechanisms appears that there is more than just a sizable correlation. Also early age confers an absolute that there may well be no exceptions to the age effect. Between the ages of 6-7 and 16-17 , everybody loses the mental equipment that requires for the implicit induction of the abstract patterns that underlying the human language, thus "the critical period deserves its name" as DeKeyser mention. DeKeyser and Larson - Hall (2005 in Dornyei 2009:241) point out, that this approach is also accepted by Lenneberg (1967 in Dornyei 2009:241) who had the original observation of the CPH that "automatic acquisition from mere exposure to a given language seems to disappear after this age". Also many scholars agree with DeKeyser (2000 in Dornyei, 2009:242) that the qualitative disparity between adult (post Critical period) and child language acquisition shows that somewhere along the line there is bound to be break that it caused from maturational constraints. Studies have repeatedly found that age causes a gradual decline in acquiring language with an attainment curve with a sharp discontinuity at the terminus of the period.
Although there is a theory 'the younger the better' whereas Dornyei points out that language learning is easier when one is young. For example a family of immigrates to a new country for a 5 year old child will be far easier to learn a L2 proficiency than the 30 year old father, but he would be better than 60 year old grandma. I can agree with Dornyei view, as for a child it can be easier to learn the second language because of the school context, but for the father it depends from the working or the environment he will be surrounded, thus it can be more difficult for older learners.
As Dorney (2009:249) explains, a young immigrant child who will start primary school in the new country at the age of 5-6, will be able to learn as often optimal conditions are provided by the school experiences. However, for an adult immigrant whose social network involve people from the same ethno linguistic group and has few native speaking colleagues at work the learning conditions are far from the ideal. It is also the same for a student that contact a L2 onetime per week in a school context.
Some other authors that agree with Dornyei, is Kuhl (2008 in Dornyei, 2009:249) who states, "There is no doubt that children learn languages more naturally and efficiently than adults" and N.Ellis (2005 in Dornyei, 2009:249) also concludes, "It is an incontrovertible fact that ultimate second language attainment is less successful in older than younger learners"
According to Gass and Selinker (2001:342) "children are more successful second language learners than adults" and there various explanations: First, there social psychological reasons why adults learn languages less easy than children. There many different versions of this hypothesis. Some suggest that adults don't want to give up the sense of identity that the accent provides them. And other suggests that adults don't want to surrender their ego in the extent that required adopting a new language, which combines with a new life-world. Second the cognitive factors are also responsible for the weakness of the adults to succeed in learning. Adults have greater cognitive abilities than children. Adopting the cognitive abilities in language learning task has less successful learning in children, which according to the hypothesis where supposed to rely a greater extent in a specific language acquisition device. Third, there are neurological changes that prevent adults to use their brain with the same way that children learn language learning tasks. This usually presented as a loss of plasticity or the flexibility in the brain. Fourth, the children are exposed to a better input for language learning thus children are provided with better data about the language.
On the other hand, some other authors disagree with that point of view and point out that 'the older the better' by state that a 5 year old student probably will occur to less progress in learning language in school context than an older learner age of 15 or 30, even 60 years old. According to Dornyei (2009:235) Anglophone children in French immersion who entered the immersion programme relatively late, around 9 to 11 years old, very quickly manage to caught up with the early immersion of students, who start he immersion programme in kindergarten or when entering the primary school. Also Dornyei (2009:250) point out that in school settings older students make better progress than their younger peers, particularly in acquiring morphosyntactic and lexical aspects of the second language and sometimes also in acquiring phonological aspects.
Also Dornyei (2009:250) states that 'younger the better' principle suggests that younger children learn 'better' in educational settings in the sense of going further but not faster. Singleton and Ryan (2004 in Dornyei, 2009:250): "Extrapolating from the naturalistic studies, one way plausibly argue that early formal instruction in an L2 is likely to yield advantages after rather longer periods of time than have so far been studied".
Over the last few years two investigations took place in Spain, to examine 'the older the better' issue. They examine three groups of Basque learners of English who attended the fifth year in primary school, the second year in secondary school and the fifth year in secondary school who had 600 hours of instruction, Cenoz (2003 in Dornyei, 2009:251) reported that the oldest group had the highest proficiency in English, followed by the intermediate group and the youngest group. The youngest learners where only better in attitudinal and motivational disposition from their older peers. The second study investigated Catalan learners of English in the Barcelona Age Factor (BAF) project and they found very similar findings. Several groups of learners (total N= 1928) with different AoA were examined three times, after 200 hours, 416 hours, and 726 hours of instruction. In the results older learners where progress faster in learning a foreign language than younger learners. Munoz (2006 in Dornyei, 2009:251) concluded that "after linger periods of time, younger starters did not outperform later starters, and the extensive span and size of this investigation makes this finding particularly robust."
However, many authors point out that in formal language contexts younger learners are not better but worse. Thus, in recent initiatives they attempt to push forward the starting age of learning a foreign language as a school productive. Lightbown and Spada (2006 in Dornyei, 2009:251), conclude that older learners are possible to achieve a better use in L2 learning in limited time. When the goal is the basic communicative ability for all students in an educational system, and when the child's native language will remain the primary language, it may be more efficient to start learning a second or a foreign language teaching later. When the learners receive few hours of teaching per week, the learners who start later between 10 to 12 years old often are likely to caught up with the learners who start earlier. Some second or foreign languages programmes that start with very young learners and provide minimum of contact, usually they do not lead to much progress.
On the other hand Ellis gives some facts of younger and older learners. According to Ellis (1994:491-492) "adult learners have an initial advantage of learning, where rate of learning in concerned, particularly in grammar. Eventually adult learners can overtake the child learners that are exposed to L2. This is less likely to happen in instructional than in naturalistic settings because the critical amount of exposure is usually not available in the former." First, only child learners are able to acquire informal learning contexts. Long (1990 in Ellis, 1994:491-492) point out that the critical period is age 6, but Scovel point out that there is no evidence to support it and argues for a pre-puberty start. Also Singletton (1989 in Ellis, 1994:491-492) point out that children are able to acquire a native accent only if they are exposed to massive L2 learning. However, some children still do not manage to acquire a native like accent possible because they try to maintain active use of their L1. Adult learners may be able to acquire a native accent if they have an assistance of instruction, but more researchers have to take place to substantiate this claim. Second, children are more likely to acquire a native grammatical competence, as the critical period of grammar may be able to be later than for pronunciation, around 15 years old. But some adult learners, might achieve to acquire native levels of grammatical accuracy in speech and writing and 'linguistic competence'. Third, children are more likely to reach higher levels of attainment in pronunciation and grammar than adults. Fourth, the process of acquiring a L2 does not really affected by the age, but the acquiring of pronunciation can be.
Beside if younger learners or older learners are better, age can affect the mastery of native like learning as we saw above. Also Mark Patkowski (in Lightbown, 1999:61-62) studied the effect of age in acquisition of features of a second language, despite the accent. He pointed that even if the accent was ignored only the learners who start learning a second language before the age of 15 they could achieve full, native-like mastery of that language. Patkowski also examined the spoken English of 67 highly educated immigrants to the United States. The learners started to learn English in different ages, but all of them lived in the United States more than 5 years. Also 15 native-born Americans English speakers of spoken English from similarly high level of education take place to the research to show the validity of the research. In the research, a lengthy interview with each of the subjects in the study was tape recorded. Because Patkowski wanted to remove the possibility that the results would be affected, he did not ask rates to judge the tape-recorded interviews themselves. Instead, he transcribed five-minute samples from the interviews. These samples were rated by trained native-speakers judges. The judges were asked to place each speaker on a rating scale from 0, representing no knowledge of the language, to 5, representing a level of English expected form an educated native speaker.
The main question in Patkowski's research was: "Will there be a difference between learners who began to learn English before puberty and those who began learning later?" However, in the light of some of the issues discussed above, he also compared learners on the basis of other characteristics and experiences which some people have suggested might be as good as age in predicting or explaining a learner's eventual success in mastering a second language. For example, he looked at the relationship between eventual mastery and the total amount of time a speaker had been in the United States as well as the amount of formal ESL instruction each speaker had had.
The findings were remarkable, because thirty-two from the thirty-three learners who start learning English before the age of 15 years old scored 4+ or the 5 level. The homogeneity of the post-puberty learners seemed that the success of learning a second language was almost inevitable. On the other hand, was a variety in the levels that the post-puberty achieved. The majority of the post-puberty learners achieved +3 level, but a wide if distribution of levels achieved. The variety of the performance of this group were look more like the performance range were expected if someone were measuring success in learning, almost in any kind of skill or knowledge Patkowski's (in Lightbown, 1999:62-63) first question, "Will there be a difference between learners who began to learn English before puberty and those who began learning English later?", was answered with a very resounding 'yes'. Thus Patkowski found that the age of acquisition is very important factor for the development of native-like mastery of a second language and that does not only affect the accent. The experience and the research showed that native-like mastery of spoken language is difficult to achieve by older learners. Also, the ability to distinguish grammatical and ungrammatical sentences in a second language seems that is also affected by the age factor.
However, according to Dornyei (2009:242) learners who are young enough in the critical period are still failing to master the L2 to a native like level. And, on the other hand are adult learners whose AoA is late, for example learners in their twenties, that has to be after the offset of the Critical Period and they succeed in acquiring native like proficiency. Also, there are evidences against the Critical Period hypothesis, an example that provided by Flege (2006 in Dornyei, 2009:242) are young learners of L2 whose L1 influence the pronunciation and it could still be detected after a long period in the host environment. And in another investigation that took place in 2007 by Jia and Fuse is that none of the ten immigrant children whose development followed by five year period in the USA manage to master the regular past tense -ed suffix at a minimum of 80% accuracy level, even thought the youngest children were 5 to 6 years old in the arrival and when the participated in mainstream schooling with additional English teaching.
Birdsong (2006 in Dornyei, 2009:243) point out that few studies that have identified in early starter L2 learners that they should achieved native like proficiency but they do not as the Critical period defeating, native like adult L2 learners has received more attention in the literature. Common figures of post pubertal learners who reach a native like level range between 5 to 10% of learners in naturalistic environments. However there are two important points that 'adults can also do it'. First, Birdsong (2007 in Dornyei, 2009:244) observed in his study that the late learners can success in phonetic training and also are having highly motivated to improve L2 pronunciation. Second, it appears that if you dig deep enough you can find chinks in the L2 armour, or even the most successful L2 adult learner. There various ways of accessing the native-like speaker judgment of L2 pronunciation, oral and written production tasks, even grammaticality judgements in more sophisticated probes such as examining subtle phonetic differences in voice onset time or intonation contour. "It seems that even if standard measures identify someone to belong within the native-speaking range obtained of performance-usually within two standard deviations of the mean rating obtained for a native-speaking norm group- more elaborate techniques can still detect subtle deviations from the native norm".
To conclude, there are many beliefs if age affects second language acquisition, if younger learners or older learners are better, if younger learners or older learners can achieve a native like language and if there is a critical period. In my opinion, learning a second language in younger age is more effective because is easier to save or remember new things, however if you are older learner there is a benefit to be able to practise the second language. And for my personal experience practising your second language and use the second language is how you learn it, instead of just learning a second language only in school context, through books, exercises, etc. In the second part of the native like proficiency I do not believe that the age matters but it matters from the person. Some people are more motivated to achieve a native like proficiency and they will try more, but other they just want to speak a second language and be able to understand them, nothing else. And for the third part, if there is a critical period, I will agree as they say the children are like sponge, I will also agree with the part that says there is a time you stop learning as I believe in some point in your life you cannot handle new things, new words or new grammar but it happen in different stages for every person.