So those relationships tend to be somewhat more unusual. I think there can be a great deal in these relationships, but it's less common because it reverses our social pattern. It's not hard to understand what somebody finds attractive about youth. Young people are beautiful. They've got great skin and lots of energy and tremendous enthusiasm for the world.
Youth is attractive, whether it's female or male.
I suspect that's because, among other things, men have a larger pool of bridal candidates to choose from. Guys can certainly, without raising anybody's eyebrows, marry somebody up to five years older than they are. They can also marry somebody up to 15 years younger than they are without anybody batting an eye. Which means their pool of marriageable candidates is much greater than women's. Women are instructed to marry somebody who is as educated or more, makes as much money or more, and is as tall as they are or taller.