I've had mixed feelings on this issue for a while. On one hand, I think there's a real danger in hiring people who are like you. I'm frequently surprised how much people defend this practice in the name of having a cohesive company culture.

Would it be more nice to have a greater proportion of older folks? I think so. The problem isn't older folks per se. The problem is just people, period. Just as much as I'm surprised by cultural homogeneity, I'm surprised by how close-minded young grads are to things they weren't exposed to in school or in youth. It's kind of baffling that by 30, a lot of programmers act like they've seen it all and done it all, and then they start snarking out on the newer, unproven languages, frameworks and platforms. It gets worse as a programmer builds up more experience to back up his case. Case in point: you ever talk to an older Lisp guy? The ones who will rip into you just for using Clojure?

In a nutshell, I think that we do it to ourselves, and it is just a matter of time, before the current crop of "young" people turn into "old" people. Mental age does not correspond to physical age, but there is a correlation, and it would lend an appearance of ageism. The problem isn't one of age. The problem is close-mindedness, and you can pin that one on people regardless of age.