I think it's evolution, conscious of it or not we are hard-wired to reproduce healthy offspring. And the chances in that area are better with young woman.
Man and Woman have different interests in that area, where man want to transfer their genes to as many youngsters as possible the woman needs protection in order to raise those kids. I'm not saying woman are less adventurous than man :-)
The female's tactic is to have fun with the good looking adventurous, challenging but not providing guy and marry the dull office clerk with a monthly paycheck. (no bad intended to woman or office clerks). Their are good well documented studies on the subject (don't have the title at hand but I'll look it up if you are interested.
So both male and female have their own hidden (even to themselves) agenda's.