I'm not sure it's that cut and dry, nor that any learning needs to be "undone". The study itself (referenced in this article) is co-authored by Pinker, and these ideas take time and research to develop.
The authors of the study under discussion explicitly claim (in the abstract even) that "the results support the existence of a sharply-defined critical period for language acquisition." You should address that argument (or cite the other "recent articles" that refute it), rather than simply dismissing it as poor statistics.
^ Basically the above study, sponsored by the NIH, found that when you correct for all relevant factors the critical period signal not only disappears but becomes anti-correlated: kids have a HARDER time in all aspects of language learning than adults, when the same level of interest and effort is applied.
So we've not only confirmed that children have an advantage, but we've identified the nature of the advantage: it's easier for them to muster both interest and effort, to the extent that this outweighs the disadvantages they have outside of those areas.
Yeah but there’s nothing physiological or neurological there, which is what the critical period hypothesis is predicting. It’s just the reality of childhood in an immersion environment.