FFXI, it doesn't require you to be in a team to level depending on your class however...it takes a long time to level solo lol it's way better in team. Though nowadays it's more about just powering to cap instead of doing the storyline etc. so it's less 'social' nowadays but it is closer than other games for the most part. The community can vary from server to server drastically...on my server (bahamut I think) the community was very good and I had a great LS I joined. Lots of older gamers.

Lineage 2 is a bit like that as well, and it's free nowadays with no catch to it. New expansion in 2 days as well, but it's almost required to level with people in that game so it sounds like what your looking for. I haven't experienced enough of the community in this game but from what I did experience everyone was really nice and helped me out a lot.

Also I doubt you'd want to play it but the old EQ is pretty social, eq2 is as well. You can queue for dungeons now on there but people are actually pretty nice in general on there so it's a lot more fun than queueing on...other games.