From what I understand, reruiters are rated based on the quality of candidates they pass to the hiring committee, so they have an incentive to only let the best pass.
This may vary depending on the office involved.
I was also rejected at the committee level, the reason was that I didn't have the amount of domain knowledge they wanted; in my case it was estimation theory/signal processing.
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.
If you got rejected by VP committee, that is unusual and work grumbling about -- and possibly constrained by amount of funding available for new hires.
The "come back in a year" is absolutely honest. Many people are hired a year, or 2, or 3 later. Google is happy to say "not sure / not yet" to people and "yes" later.