I'm in my mid-30s now, and I know some people who are, or at least were, really good programmers. But I was amazed recently when they didn't really know what Ruby on Rails was, or django, or AJAX. I'm not trying to play buzzword bingo here, and I certainly don't think people need to know these things in detail, or agree that they're good tools. But it is very alarming that they draw a blank. These aren't obscure technologies - if you haven't even heard of them, you clearly aren't paying attention.
I suppose the 30+ set could get insular enough that nobody brings these things up.. whereas it's nearly impossible not to learn about them if you hang with a younger crowd.
That said, I had a professor in college who was over 70. He could write programs on the whiteboard that would compile without a single syntax error - it was bizarre. He was unbelievably up-to-date. And it wasn't out of some kind of old man and the sea stubbornness, it was just deep in his personality to keep reading, hacking, knowing what's up.
You can't tell who has a drinking problem in college, because everyone drinks too much - you have to wait and see who's still overdoing it 10 years later. By the same token, maybe you can't tell who the true hackers are until they've considered and rejected the opportunity to fade away...