I was a bit pissed that the way the recruiter told me initially I thought the hiring committee was just a safety check and pretty much a rubber stamp so I got all excited for abut a day until he told me I didn't pass the committee. He gave me no feedback whatsoever about interviews or anything, just encouraged me to apply in a year, which may be standard talk for all candidates (he did invite me later to an online seminar so there's hope).

The way I understand it now is that besides gauging your expertise level and general review they may simply select the top X for the positions they have, given a larger number of candidates that passed the interviews.

I didn't see anything that seemed to discriminate by age. One interviewer was a woman in her 40s ro 50s. That said it is true that Silicon Valley (I also interviewed for Facebook) is all white or Asian men in their late 20s or early 30s, (with some sparse women). I saw literally zero black people in three days in SV and the only obvious Hispanic were the staff at my hotel.