The extent to agree with the notion that language develops according to Chomsky’s language acquisition device will depend on age, though LAD relates to Chomsky's postulate that language acquisition of syntactic structure from impoverished adult language input occurs because of innate finte core dimensions of langage knowledge that Chomsky called Universal Grammar.
Although widely recognized, particularly in language training programs, Chomsky’s viewpoint depends on stages of language development that correspond fairly closely to stages of child development.
At the time that the ideas of Chomsky and others gained credence, human development stages were viewed as fairly concrete. In other words, once one passed certain stages optimal for learning, that stage could not be revisited. In that case, older children or adults could not acquire new language, at a minimum not very easily. Today, however, the human brain is now understood to be elastic and ever-changing.
Although ideally it is certainly preferable to learn or at least to gain exposure to new languages as a child, more recent studies in linguistics show that adults can acquire new languages. So the extent of agreement with LAD depends upon acceptance of the postulate of Universal Grammar governing an innate core of universal language syntax.
Below are some links describing language acquisition in children and in adults