I wouldn't equate looks with desirability, for men it's much more complex because women have complex expectations, and that's exactly why men maintain and even enhance their desirability with age.

That being said, the desirable men are either committed (unavailable) or available because they can hop and choose to do so. So only a minority of desirable men are available. This is in strict contrast with the large majority of young women, who can almost always hop relationships should they so choose. Since overall there needs to be gender equilibrium, females are sliced by age to a much larger degree, allowing the minority of desirable men of all ages to pursue the minority of younger women.

The asimetry is caused by the fact that females are selective and males are partner-maximizing. It's not good or bad, it's a sociological truth.