How old are Warren, Andrew and Jonathan in Season Six?    Is Jonathan the same age as Buffy?   Any help appreciated.

Jonathan was in the same class as Buffy and co., while Andrew's brother Tucker was the kid who raised hell hounds for prom, so Andrew is the youngest.  I think Warren was older, as he seemed to be further in his studies (like maybe a junior or senior in college) in "I Was Made To Love You."

Jonathan graduated the same year Buffy did, so I assume he's around the same age as her. As for the others... I was always under the impression that Andrew was a little younger, and Warren a little older, but I don't know if there is any basis in canon for that, or if that is just my assumption.

 Thank you both.  So that makes Jonathan 21,  Warren 22 or 23 and Andrew, say 18 or 19 in Season Six.   Is that about right?

Or Andrew could just be one year behind, but yeah. Scoobies were 21 by end of Season 6. I don't think Andrew was that much younger (Tom Lenk doesn't pass that young to me.)

From the Buffyverse Dialogue Database:

Willow: Hey! I think I found him. A Warren Mears. He went to Sunnydale High with us for a semester, and then he went to the tech college over in Dutton. I've got a local address where his folks still live.

So, Warren is probably a year or two older.