Ironman's about 2 years older than me. I've tended to date guys older than me, the one time I dated a guy younger than me was a disaster (granted, it was in High School, where younger boys ACT exponentially younger.)
I probably wouldn't date someone younger than I, and as far as older, probably up to like 28.
My friend is 20, and when she was 19 she started dating (and moving in with) a 32 year old. I've met him, and I've seen them together, and it's really weird; they're both so much alike. She's so mature for a 20 year old. It's interesting, he's actually very similar to her mother, who passed away a few months before Cate (my friend) met Matt (her man-thing.) In most situations, I think people would be pretty convinced that he just wanted some tight virgin poon, but I've seen them together, and it's definately genuine. [another side note, her mother was much younger than her father, as well]