Secondly, there are many factors affecting the effect of second language acquisition, such as attitude, learning motivation, learning methods, environment, age and so on. However, age as an unchangeable factor is one of the important factors affecting the second language acquisition. As to the role of age factor in second language acquisition, Lenneberg put forward the term critical period hypothesis in 1967, so there was a common belief that the children were much easier to learn foreign languages than others. Because the differentiation of brain in childhood has not been finished with strong plasticity and flexibility, learners could quickly and easily absorb new language information. Due to it, kindergartens and primary schools have opened the English courses, even there are lots of English training institutions. But the effect of learning English was unsatisfactory.

Could age factor explain the second language acquisition? Academic circles always hold two attitudes: one thinks children who learn English early are better “the younger, the better”. The other doesn’t think so. It shows the complexity of age factor. Through the experimental investigation on non-English major students, the author points out that age is not the decisive factor affecting the second language acquisition but it’s one of the important factors. The purpose of the paper is to understand the relationship between age factor and second language acquisition, reduce the pressure on students from primary and middle schools to learn foreign languages, guide students to learn foreign languages according to the characteristic and laws of all age and point out reasonable learning strategies.  

II. Critical Period Hypothesis 

2.1 The Definition of CPH

    What is a critical period? It is said that there is a specific and limited period for language acquisition. The critical period hypothesis was first introduced by Penfield and Robert (50). They assumed that the children’s brain had plasticity especially in acquiring language, and the brain would lose its plasticity gradually. A child could learn a second language as easily as the first language before the age of nine. Penfield and Roberts deemed that the critical period was the age of 2 to 9 (Penfield and Roberts, 131). After the key period, people would feel difficult for language acquisition. They stated that there were differences between children and adults in the neurological basis when the right hemisphere of the brain was damaged. Children may lose their ability to talk while adults would not. On the contrary, when the left hemisphere of the brain is damaged, children’s speaking ability is unlikely to be affected, but adults may lose speaking ability completely. 

    In 1967, Lenneberg presented the term critical period hypothesis, which explained children’ faster and successful attainments over adults in second language acquisition. Lenneberg stated that language was the production of the brain, and the brain of children who were 2 to 12 years old had very good plasticity. Before puberty, the two hemispheres of the brain are involved in language learning. People could naturally and effortlessly obtain language. After puberty, most people’s brain has lateralized and their neurological system has lost such plasticity, which leads to more difficulties for language acquisition. Lenneberg also pointed out a view of the critical period hypothesis that children may not get the first language if they did not contact with language before a certain age, given as puberty. Meanwhile, this view could be tested by the example of Wolf boy.