I've been pretty serious about this too, Steve.
Shouldn't the first question be whether or not you want to grow up?!
TH said it best. Release all the money-sucking contractors that keep your home & car running and learn to do it for yourself. You may not want to be a handyman or overhaul your own transmission, but if/when you grow up you'll be able to take care of many things for yourself instead of depending on repair companies.
You could try taking temperament/interest surveys and skill assessment tests. Several of them are on the Internet, especially the ones that help you decide your type of personality. I'm a little jaundiced on the interest surveys & skill-assessment tests because they claim I'll make a wonderful nuclear engineer-- just the job I was trying to get out of. OTOH this self-assessment could happily consume several weeks/months.
You could try new things. I'm lucky enough to have a kid that drags me along on the quest to do everything under the sun, but I've learned some skills that should serve me well as my body ages-- surfing & tae kwon do. (Neither of these existed in my Pittsburgh neighborhood when I was growing up! And I never "had time" for them during my working years.) Or just get better at the things you enjoy and now have the time for. In my case that's been home improvement and bicycling.
I've read "Do What You Love, The Money Will Follow" by Marsha Sinetar. Bleagh. I've also read "What Color Is Your Parachute" by Nelson Bolles. It's good for those temperament evaluations and basic interest surveys, and even if you're not looking for a job it might trigger an "Aha!" moment.
You could also read Paul Terhorst's "Cashing in on the American Dream: How to Retire When You're 35." One of his best pieces of advice is "Change nothing for at least the first two years." IOW, enjoy retirement without trying to turn it into a new job. He also has the world's best answer for that eternal question "But waddya DO all day?!?" at
http://www.geocities.com/TheTropics/Shores/5315/bodywork.html .
But the best book I've read is "What Should I DO With My Life?" by Po Bronson, a world-class modern writer.
http://www.pobronson.com . The paperback expands/updates the hardcover but both are quite entertaining & thought-provoking.
After years of soul-searching (and two years of ER), I've realized that I'm never going to grow up and be anything other than what I am right now. I'm happy exploring whatever interest comes to mind that day and pursuing the thread as long as I'm interested. I'm especially happy watching my kid grow up, become independent, and get ready to flee the nest. Otherwise my honey-do list doesn't seem to be shrinking, my reading list is growing, and my "I'd like to try that someday" list is exploding. If I drop something, I keep track of where I left it because I know I might be interested in coming back to it in a few months. The years have flown by and, like most of the ER posters here, I can't imagine how I ever found the time to work.
So you could try something that's very difficult at first-- relax. No one's keeping time. Next, try pursuing an interest (it really doesn't matter which one), and see where it leads...