My character is young chronoogically, but for the time she lived in she's already considered an old maid.  I mean people got married when they were like 13, and 40 was considered really old.

I don't think younger characters have the most growth.  I think, however, that the older a character is the more work has to be put into his/her history, and the more difficult it becomes to justify a character without a lot or pre-existing close personal attachments.  (It's way easier to justify going on a quest if you don't have kids and a mortgage.)