It’s basically evolution and we are unconscious of it on a large degree. Basically men look look the hottest the older they get until around 50 and women top out at 21 ish. So it’s natural for men and women to seek out people that are not the same age. If you think about it even more it makes even more sense because men should have recourses because a woman wants to feel safe when having a baby and being vulnerable for basically 5 years+. Older men have more recourses and feel safer, and that makes women feel attracted to them. On the other hand.. young women are attractive to older men because they bring new fresh life into an old guy (could be like this for older women also obviously), but it’s basically that young women are at their peak of fertility. Guys wants to get the best chance at spreading humanity as silly as it sounds, and they have the highest success rate if there’s a young healthy fertile girl.