Some interesting points made here in these comments, worth rebutting.
1. older folks are less flexible, can't relocate, etc. When we have kids in high school, that's valid. But high school doesn't go on forever.
2. older folks cost more. You'd be surprised. Salary doesn't have to be an always-upward ratchet. There are plenty of us who are able and willing -- even delighted -- to work for less than the executive-level pay of the biggest jobs on our resumes.
Unlike many of our juniors, we aren't scrambling to pay off our edu loans any more, nor are we scrambling to cover those costs for our kids, or pay big mortgages.
You know that dream about being motivated by the work, not the money? It's a real thing. Many of us are living that dream.
3. older folks are a protected class (in USA, anyhow). That's true. We are nominally harder to lay off when things get rough. But we've been through a few cycles of things being good, then bad, then good, and we've survived. We are as willing as anybody to stop drawing our pay when things aren't going well. Some of us are willing to agree to that in advance. Ask whether we'll accept contractor status, rather than employee status.
See item 2 about being motivated by the work.
4. older folks drive up health insurance pool costs. true. sucks. But I, for one, am on my spouse's insurance so the startup I'm with doesn't have that problem. Many of us have similar setups. You can't ask in an interview, but we can tell you voluntarily. Plus, when we hit 65 (in USA) we go on this decent national single-payer health plan and out of your pool altogether.
5. older folks can't manage 80-hour work weeks. Of course we can manage crunch time. We've done a lot of it, and we're skilled at getting it done.
Can we manage sustained 80-hour weeks for years at a time? No. Neither can you and keep your quality up.
6. older folks' skills are obsolete. Not true. Maybe that was true once, but many of us put a lot of work into keeping up to date. Safari Books Online, and online tutorials, and community / dev versions of various tools, have made that possible.
7. older folks would rather play golf than work. For many of us, that's just nonsense.
So, don't just screen out that resume showing a MS degree from 1980. Take a look.