Actually smoke, young women prefer older men, but once they hit a certain age (early 30's or so) they start prefering younger men. It's the same with men, young men prefer older, more experienced women, but again once they hit a certain age (which is later than women) they start looking for younger women.

I think it has to do with trying to feel younger by being with a younger person (a 50 year old man wants to feel in his 20's again) or feeling older by being with an older person (a 20 year old guy wants to feel more like a man in his 30's).  

I'm not always right, but I'm never wrong -Garfield