Human children takes over a decade to become adults, so it is pretty likely evolution selected for women who stopped getting pregnant once they neared the end of their lifespan. Producing kids is super expensive so better take care of those you already have at that point.
> Why is the sterotype that youth is very attractive in woman, but the same sterotype doesn't apply to the same extent in men
Reasonable theory: Women mostly select men with good genes. Men mostly select women who can get pregnant and survive said pregnancy and bring the kid to adult. The main predictors for a woman being able to get and survive pregnancy is that she has a flat stomach (so not already pregnant) and she is young and healthy. Also existing kids will hurt your kids so better select a woman who doesn't already have kids, which historically meant young women.
Good genes is much more complicated, age is a positive factor here since it means the man could survive for that long but there are all sort of things women could look for here.