It is very common knowledge that it can last through adulthood. Any ADHD site will say this. The question is does he know this, or is he refusing to deal with it? I have plenty of places for more info. If you need it. And there are some great adult ad/hd sites like http://jeffsaddmind.com/for-first-time-visitors. Which he should find very helpful!
I had a friend who's daughter was ADHD. If she missed her meds one day only, she would think she was fine. She got mixed up with gangs. They got her out and she would do well and then the samething would happen over and over. After she graduated she ended up PG. A few years ago I heard she was doing very well. For her it was a matter of maturing and acceptance. Thank you for the link Sandman