A 23-year-old just out of college acts exactly the same way as a 20-year-old in college. There's literally no difference.

I get the difference in experience and where you are in life is a factor, but the issue is people presume the existence of that factor outweighs all others, and that it can only result in a negative.

Can you give me an example of actual harm being done to the younger person in a gap between high school and college? Harm that applies near universally, to every young person, if they ever enter a relationship with someone that is only a single major life experience ahead of them?

Harm can be done, obviously, but it's about the circumstances of that specific relationship. There's no reason to presume it as a rule in a case like this.

It also makes an unfair presumption on both parties: that the older person is irresponsible and manipulative, and the younger person is immature and vulnerable.

It really is kind of odd how much we talk about this topic without appreciating that at a certain point we are almost infantilizing young adults. We agree they're old enough to vote, own a gun, smoke, and drink, but we can't give them the the courtesy of respecting their decisions on who they want to sleep with? They're not actual children.