My guess is that the Y combinator partners evaluate each team themselves, rather than having an Arc program do it. So while they may have an average they gravitate towards, they probably would be willing to consider teams outside of that if they're impressed. Being a team does seem to be one of the 'rules' that they aren't as flexible about.

Yes; we've had several people in their 30s. We get a lot of people in their early 20s, but that's probably just because more of them are starting startups.

And paying attention to Y Combinator.