I'm a straight man, and the absolute youngest age of a woman I would date is 21 years old, but I would want her out of a traditional college student environment, and more into a young career environment. Realistically, the youngest woman I could see myself dating is 25 years old.
I didn't include 70 years old (and older) in my poll. If people 70 years old, and older are too young to date, then you're too old for dating, or you need to seek therapy.