Could he have adult ADHD?

-he changes his job about once a year
-he always changes subjects a lot in our conversations, and when i need him to be serious i have to constantly remind him (i have to be like babe we're talking about this not that) about every 2 or 3 minutes
-he has trouble in school, he thinks hes stupid, but i know he is smart and understands most of the stuff
-he drives really fast
-he likes to act spontaneously
-he gets bored easily
-he has trouble concentrating on "boring" things, he can play guitar hero fine though
-he told me himself he thinks he has some type of disorder

any comments or suggestions would be great, thanks

This describes many, many people. Yeah, he may actually meet criteria for adult ADHD (maybe), but how useful is that diagnosis when at least a 3rd of the population would also meet criteria? In the DSM IV TR, the criteria are listed for children (many pertain to school settings only). Its often difficult to apply these criteria to adults. It's primarily a disorder associated with school-type difficulties.
He needs to learn to be more responsible, really. ADHD or not ADHD. Sadly, stimulants aren't as helpful for people who don't have to sit in class all day. I'll agree that he is impulsive and could probably get meds (he'll have to prove he had ADHD as a child, though, unless you get a pretty lax doctor).
I just think he needs to grow up, and therapy may be helpful for him. But I don't think conceptualizing it as a disorder is helpful at all.

Not too sure, but try some focusing supplements... a few have helped like focus fast.