Then I went to work for a pretty cloistered company for the next eight years. One closed local office and one declined offer to move to HQ later, I started looking around. And suddenly found myself the oldest person in the room.
I had done contract work for many of these companies prior to 2000, often for the very same departments or groups. The irony of the situation is the lead and management positions which had been filled by guys in their late 30s, 40s and 50s, were "now" filled by guys in their late-20s and very early 30s. And the difference showed.
This is in the Midwest, so ageism isn't just a SV thing.