I've met developers over 50 who were passionate not only about their job but about their prospects for learning new things. I think that's a character attribute that you either have or don't have, and I don't see a lot of evidence that it fades with age.

I have also met a lot of developers who are passionate about the lifestyle features of being a startup software developer but who are also willfully stuck in ruts like spending months cultivating positions about which testing framework best expresses the right testing methodology, or whether HTML is best generated serverside or clientside. They don't read papers, they plan on maybe one day learning C, but they wear the right t-shirt and are on the right IRC channels. These are things that might matter a lot when you're just starting out in your career but don't so much matter at all when you've got your sea legs.

There are a lot of those people and I think that may color our impression of which age bracket is most engaged.

The older programmers I know are in niche fields, like audio effects processing or hardware hacking. It's not a job, it's what you get up and do with your brain every day.

In other words, the interesting stuff! :)

Something's level of interestingness is more a decision on my part than a property of the something, I've found.