I’m around the same age group as the above commenter described, and I can confidently say “not being supportive of dating someone significantly younger than yourself” at our age is looked frown upon. We usually joke about “lol i can’t imagine having anything common with 21 year old self, and as a self respecting person, i wouldn’t date one either”.

I think it’s a cultural thing, and personally I wouldn’t judge two of-age people making their own decisions. Really depends on your group dynamics and groupthink.

Also, not every co-ed friendship is rooted in jealousy or sexual desires.