Being a near 15 year experience software developer who turns 40 later this year with a wife and two kids I can see many sides to this debate. Personally I've found that as long as I stay on top of technology, limit myself to a single industry (to become an industry expert), write quality code, and try to be someone people want to work with on a personal level then I don't have issues finding employment. People seek me out. We'll see if I'm singing the same tune in 10 years after my partially gray head is fully gray.