The "age" I go for:
At least 21, out of college or almost done if not, mature, and values individuality. Not the crazy, always-get-drunk, make-out-with-everyone type either.
Upper-limit is mid-30s. I'm 30 and anything passed 35 would seem strange to me. More likely than not, I'm sure the feeling would be mutual.
If I had to narrow down my preference further, it would be probably be mid-20s to early-30s but nothing is set in stone. Whoever's compatible personality-wise and looking to establishing themself, like I'm trying to.