You specifically asked why "some men" only date younger women. I answered your question.

You're getting ME mixed up with "some men," I never said I would only date a younger woman.

The upside to dating an older woman could be more life experience, knowledge, and therefore better conversation, common interests and references etc etc.

And, to your point about women, it's not like women don't care about mens looks and health at all. They are hardwired for it just like men. But they put more emphasis on a man's resources than his looks.

Also, I don't think men being attracted to younger women is an "outdated" instinct--any more than preferring new clothing over used clothing. Many women share the same attraction for younger men for just this reason.

It's kind of the wild west now in terms of relationships, where your personal circumstances and desire for happiness carry a lot more weight than the societal pressure to marry young, have kids, and settle down does.

Staying with one person from your 20s until you die in your 80s or 90s continues to make less and less sense.