1) Older programmers won't put up with bullshit. They expect to have reasonable goals, be listened to, be compensated fairly, and have a reasonable schedule. They've been around the block enough to identify bullshit and will leave when it starts getting too high.
2) Older programmers really don't always understand the "cool" social crap that teenagers are into this year (for good reason--most of it is garbage). Unfortunately, most of what Silicon Valley is interested in is "cool" social crap so that they can get a big buzz and flip the company to Google or Facebook.
Funnily enough, companies that value that silly thing known as "profit" are quite happy to hire older programmers. It's just a function of Silicon Valley not believing in profit that is causing the ageism.