This is an interesting question and one I've thought about a lot too. I'm 37 and an experienced developer/entrepreneur. I've been self-employed for 12+ years but if I ever had to "get a real job", it's something to think about. First off, remember that it's not legal for a US employer to ask your age. They can only ask if you're over 18. Of course, if you want to be sly about it, you'll need to craft your resume care…
Just to clarify on the legal distinction: They can ask, and you can answer or not. What's illegal is making an employment decision based on age. Of course, the most foolproof way to prove to a belligerent labor attorney that age did not drive an employment decision is to never possess the age information in the first place. So nobody asks, and any company big enough to have an HR department internally forbids it from asking about age or any other protected factor like national origin and religion. But it's not illegal simply to ask.
Also, the Age Discrimination in Employment Act only protects workers over 40. 37 is actually fair game for discrimination.
Citation for both of the above: http://www.eeoc.gov/facts/age.html