From Wikipedia: The Critical Period Hypothesis states that the first few years of life constitute the time during which language develops readily and after which (sometime between age 5 and puberty) language acquisition is much more difficult and ultimately less successful[1]. The critical period hypothesis was proposed by linguist Eric Lenneberg in 1967. Evidence supporting this hypothesis comes from feral children who failed to develop language after being deprived of early linguistic input. The most famous cases are Genie and Victor of Aveyron. However, it is also possible that these children were retarded from infancy and abandoned because of this, or that inability to develop language came from the bizarre and inhuman treatment they suffered.[1] Other evidence comes from neuropsychology where it is known that adults, well beyond the critical period, are more likely to suffer permanent language impairment from brain damage than are children, believed to be due to youthful capabilities of neural reorganization.[1] The nature of this phenomenon, however, has been one of the most fiercely debated issues in psycholinguistics and cognitive science in general for decades. [edit] Second language acquisition See also: Second language acquisition#Critical period research to date The theory has often been extended to a critical period for second language acquisition, although this is much less widely accepted. Certainly, older learners of a second language rarely achieve the native-like fluency that younger learners display, despite often progressing faster than children in the initial stages. David Singleton (1995) states that in learning a second language, "younger = better in the long run," but points out that there are many exceptions, noting that five percent of adult bilinguals master a second language even though they begin learning it when they are well into adulthood — long after any critical period has presumably come to a close. Evidence is controversial the Second Language Acquisition involves a critical period, nevertheless, it is generally agreed that younger people learning a second language typically achieve fluency more often than older learners. Older learners may be able to speak the language but will lack the native fluidity of younger learners. The Second Language Acquisition Critical Period coincides approximately with the Formal Operational Stage of Jean Piaget's theory of cognitive Development (Age 11+).

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Hello Cherry ;) Here are some links and references on the subject: Critical Period Hypothesis on Second Language Acquisition: * http://tesl-ej.org/ej14/r14.html * http://www.stanford.edu/~hakuta/Publications/(1999) - CONFOUNDED AGE LINGUISTIC AND COGNITIVE FACTORS IN .pdf * http://www.ncbi.nlm.nih.gov/pubmed/2920538

# [PDF] Second Language Acquisition and the Critical Period Hypothesis File Format: PDF/Adobe Acrobat - Quick View by D Birdsong - Cited by 271 - Related articles The debate over the critical period hypothesis embodies some of the most basic questions about second language acquisition, and indeed, ... www.stanford.edu/.../(1999)%20-%20CONFOUNDED%20AGE%20LINGUISTIC%20AND%20COGNITIV... # Second Language Acquisition and the Critical Period Hypothesis by D Birdsong - Cited by 271 - Related articles Second Language Acquisition and the Critical Period Hypothesis ... of the Critical Period Hypothesis, but a number of different versions of the theory). ... tesl-ej.org/ej14/r14.html - Cached # Second Language Acquisition The only conclusive evidence for the critical period hypothesis with regards to FLL is ... According to this hypothesis language acquisition occurs in a ... chris1066.tripod.com/theories.html - Cached - Similar # Second language acquisition and the critical period hypothesis - Google Books Result David Birdsong - 1999 - Education - 191 pages As the papers encompass many domains of inquiry in L2A--syntax, morphology, phonetics/phonology, Universal Grammar, and neurofunctional factors in language- ... books.google.com.au/books?isbn=0805830847..