This is a great rundown! One interesting thing that comes to mind is that most of the recent research I've read says somewhat counterintuitively that the age f

This is a great rundown! One interesting thing that comes to mind is that most of the recent research I've read says somewhat counterintuitively that the age factor is not as big of a deal as you might think[1]. I was taught at University that there is a critical period age after which it becomes much more difficult to acquire a language, but there is actually little evidence for this. Aside from accent acquisition, which does seem to be linked pretty tightly with age of exposure, the biggest difference generally between adults and children in language acquisition is the amount of time they have to learn it. Some studies even suggest that children are worse at some aspects of acquisition[2]. As you said, adults are busier, which is the biggest difference. [1] Hakuta, Bialystok 2003 [2] Ferman, Karni 2010