Definitely brain plasticity is real, but there are people who learn to speak languages as adults, with native proficiency. I recall hearing on the radio, peopl

Definitely brain plasticity is real, but there are people who learn to speak languages as adults, with native proficiency. I recall hearing on the radio, people in India who (as adults) learned a Midwestern US accent, because they were doing phone support and they could get through each phone call quicker if the old person on the other end of the line wasn't confused by an Indian accent. I am a midwesterner, and I could not detect anything "off" in their midwestern accent, even though I knew they were Indian. In other words, you can only learn a language natively, if you have some good reason to do so, like say money. But, your basic point that both effects have something to do with it, is surely correct.