The Critical Period Hypothesis refers to the idea that the ability to acquire language is related to aging and there is an ideal period of time to attain a language, after which it is no longer possible. This hypothesis was originally proposed by Penfield and Roberts (1959) and followed up by Lenneberg (1967) who suggested that it could be extended to the second language acquisition. Subsequent studies all found the same result that second language learning performance correlates negatively with the age at which the learning begins prior to puberty. Contrarily, among late learners, the correlation of age with learning performance suggests that different mechanisms are affecting adults proficiency other than maturation (Birdsong & Molis,2001; Hakuta et al., 2003; Oyama, 1976). However, it is controversial that this negative correlation between age and learning performance can be attributed to a biologically based critical period for second language acquisition that prevents older learners from achieving native-like competence in phonology as well as syntax of a non-native language.