I have to tell you that MOST of the guys I know that are near my age are guys that I would NEVER date. In my experience, 21-year-old guys are not the sort of guys with whom I want to hang out, let alone seek a relationship.
My last relationship was with a man 14 years older than me, and I never thought about the dirty-old-man thing. We definitely had age-related issues, but the actual fact that he was significantly older than me never crossed my mind until after the other problems arose.
I think mid-30s is definitely an acceptable age to keep in the man-pool for me...
(no offense to early 20s men, I am sure that I have just met the wrong ones...)