What are their ages at the end of season 12?
Andrew - isn't specifically with anyone but nothing contradicts my head canon that he got together with Clive at the end of season ten and they're still together.As of the end of S12:
Buffy is single after breaking up with Spike.
Willow is also single and seemingly has been for a while.
Xander is with Dawn and they have a baby together.
Giles is now an adult again but also single; no sign of Olivia or Roux (thank god!)
Faith is single. She has been ever since breaking up with Robin Wood pre-S8 (good going Robin, you really did a number on her!)
Andrew; don't know, don't care. But he is out and happily gay.
Hope this helps.
Buffy's 30 so it's 2011 to 2012.I don't know. Go to Buffy wiki and skim the bio of each character. It should give you a pretty good idea., at least with a little math. I don't read those comics myself, though, and consider them a different universe than from the show for multiple reasons.
Maybe someone here can give the year in the Buffyverse in which the last season ended?