At what age, approximately, is the end of the critical period for native language acquisition?

Of course, I understand that many details surrounding the critical period are up for debate. I want to know after what age is it a pretty safe bet that a second language could not be acquired with native fluency. Any references associated with estimates would be much appreciated.


4 Answers 4


The usual limit is considered to be between the 3rd and the 4th year of age (I've also seen only the 3rd year being mentioned, but well, we're still around that time).

There is a mention about this on the wikipedia page for Sequential bilingualism, but there is a document that treats it more in depth: "Incomplete acquisition in bilingualism: re-examining the age factor" by Silvina Montrul.

  • 1
    I do not think an answer simply glossing over the extensive criticism regarding the critical period (see the other answers) is a good answer. I also don't think an answer accepting at face value that there is a single time point marking the end of the critical period is a good answer, considering the critical period is almost always, even by those defending it, understood as a characteristic of a curve, not a one-dimensional boundary..
    – user3503
    Jun 14, 2014 at 14:10
  • @user3503 All the answers basically "gloss over" the criticism regarding the critical period. I don't see that much of a difference. Also, my answer does not provide a one-dimensional boundary but provides a range of about one year of the most common limit given for first language acquisition.
    – Alenanno
    Mar 22, 2015 at 18:55
  • That doesn't mean this answer should be excused for also glossing over more modern perspectives. And you're very much implying a one-dimensional limit (a boundary), whereas current thinking assumes an asymptotic, smooth, not too steep gradual decline.
    – user3503
    Mar 23, 2015 at 10:34
  • @user3503 That's what you're interpreting, not what it says or what it implies, since my answer clearly states a range of at least one year. You could say that it's too short, but again, my answer does not state that that's the only correct answer. I only gave the most common time limit. If you think my answer is ambiguous, I can highlight the fact that there is no ultimate consensus.
    – Alenanno
    Mar 23, 2015 at 11:07
  • This is the sort of claim that may be supported by scholarly research, but is obviously wrong. There are thousands if not millions of people who speak a language natively who only started at age 5 or 6. Most people who live in a place with lots immigrants (e.g. large cities in the US, Canada, or Australia) probably know at least one living, breathing counterexample.
    – Aqualone
    Nov 21, 2020 at 4:16

Notice that not everyone subscribes to the Critical Period Hypothesis.

No robust empirical evidence supporting various CPH theories is available at this point.

Here's a very good quote from an excellent textbook written by Lourdes Ortega:

"An early start does not guarantee complete and successful acquisition in all cases, as some children who start learning the L2 at an age as early as four or even two may be found to differ from native speaker performance in subtle ways" (Ortega 2009, p. 29).

See chapter 2 with an excellent summary and annotated suggestions for further reading in Ortega, L. 2009. Understanding second language acquisition. London: Hodder Education.

Also, see a recent monograph by Herschensohn, Julia. 2007. Language development and age. Cambridge: Cambridge University Press.


There is a great deal of individual variation but most textbooks place it much later than the original responder, up until puberty (say, between 10 and 14). This is certainly true, as you ask, for children acquiring a second language. It's less clear what the critical period is for children who began their life with absolutely no linguistic input from any language (e.g. `feral children').

  • Can you provide some reference for that?
    – Alenanno
    Oct 8, 2011 at 9:11
  • 1
    I mentioned textbooks; some examples are Fromkin, Rodman & Hyams' An Introduction to Language and OSU's Language Files. I imagine these books will have more detailed references. I believe that the 3/4-year limit is true for 1L acquisition; I only corrected your answer because it appeared as though the questioner was interested in 2L acquisition. Oct 11, 2011 at 20:52

The notion of critical period that you use in your question (viz. difficulty of second-language acquisition) also goes by the more neutral name "age effects". At least some researchers (e.g. Kathleen Currie Hall in this abstract [sorry no link to paper at hand]) don't believe that there is any a priori basis at all for putting an upper bound on the critial period.

In short, there is perhaps no age at which it is a "safe bet" that a second language could not be acquired with native fluency (barring e.g. silly things like exposure at an age so advanced that death is statistically likely to come sooner than L2 acquisition).

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