Clinically speaking, one cannot "develop" ADHD in adulthood. It is a diagnostic requirement that symptoms be present before the age of 12. I dislike how the article uses the terms "outgrows" and "recovered" when referring to adults who no longer exhibit problematic symptomatology. This group no longer has a clinical level of disordered behaviour (as in, the last "D" in ADHD) and has not necessarily "recovered" nor "outgrown" a disorder.
The second part of your question is complex. I will say that brain chemistry changes throughout ones development and neuroscience has a much better understanding of how that works. Though, we are far from a succinct explanation of how it all fits together.
The second part of your question is complex. I will say that brain chemistry changes throughout ones development and neuroscience has a much better understanding of how that works. Though, we are far from a succinct explanation of how it all fits together.