The Davidson Institute reports that they get a reasonable number of queries from grown-up gifted kids who say they never knew that was what was "wrong" with them. (See this article by D. Lovecky for a round-up of the personality characteristics -- positive and negative -- many gifted adults display.) Some schools are simply uninterested in figuring out why the quiet kid in the back is bored with school, or doing anything about it. If parents don't know how or can't nurture their children's gifts, and if the child doesn't speak up or find mentors or teacher that do understand, then the kid can grow up thinking "learning isn't for me."
That's a sad situation. Fortunately, adults can control their lives in ways children can't. That means that adults who realize that maybe they weren't dumb, or weird, but just weren't being challenged, can create situations where they can feed their brains. Many, as the Lovecky article notes, become entrepreneurs. When you create the work rules, after all, you don't have to play by the ones you never liked in school. You can seek out creative fields and workplaces, especially ones that tolerate difference. You can create environments with intellectual peers by joining organizations such as Mensa and participating in their forums and activities. You can form book clubs and philosophical societies that draw people with intellectual interests. And you can always seek out activities like crosswords and auditing college courses or taking them online to keep your brain buzzing.
I'm curious if other people have suggestions for adults seeking to nurture their gifts.