A long time ago, I read The Language Instinct. Inside the back page of my book are notes with page numbers. This is a practice I learned from a book by James Michener. At some point, I started sharing in conversations something I learned. Unfortunately, I had not made a note for this that I could check and the information was more complex than I remembered. Since I had shared this more than once, I thought I should really find the reference and it was not easy but I found it on page 293. The first part I had right.
In sum, acquisition of a normal language is guaranteed for children up to the age of six, is steadily compromised from then until shortly after puberty, and is rare thereafter.
Here is the part I screwed up.
We do know that the language-learning circuitry of the brain is more plastic in childhood; children learn or recover language when the left hemisphere of the brain is damaged or even surgically removed (though not quite at normal levels), but comparable damage in an adult usually leads to permanent aphasia.
While this itself is fascinating to me, I had been embellishing the story to say language is acquired in the brain’s right hemisphere in children and the left for adults. Now that I’m rereading it after so many years, it is clear that the book says this can happen but is not necessarily so.