[Veelox]

I think a big part of that is age of child birth. If you start having kids at 22 it's straight forward to end up with 5 before you are 35. If you try to have your first at 35+ you may have to get fertility treatment if you wait longer or want multiple that are spaced out.

[joenot443]

I think you hit the nail on the head. The small-town, big family folks I know (my parents included), all started their families before 25. It's the double professional degree couples with a late start who end up at the fertility clinic, and tragically, are incredibly more likely to produce children with complications.

Even now, as someone who's 27 and looking to start a family before I'm 30, I'm having to be more discerning with age when picking a lifelong partner. My women friends haven't been especially supportive of this strategy, and I can see it when I introduce them to a date a few years younger than them. Call it selfishness, call it pragmatism, but when it comes to the health of my future children, I don't mind being choosy.

[krageon]

If these women are younger than them, I think the judgement can be safely categorised as jealousy. The fact that you're picking partners younger than them makes them feel like they're not good enough, which is why they are upset. That doesn't make you selfish - you don't exist to make others feel good.

[kredd]

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.

[pclmulqdq]

This is it. Evolutionarily, 30-35 is extremely late for procreation in humans. That doesn't give you enough time to raise them before you die at around 45 (around the life expectancy of wild humans).

[amanaplanacanal]

Life expectancy at birth, maybe, but if you lived long enough to reproduce your life expectancy was much longer than that.

[pclmulqdq]

That's true of most of the civilized period when humans were relatively safe from predators. Most of human history was not like that. As far as I know, hunter-gatherer humans without this form of safety generally didn't live past 40 except in exceptional cases, even if they survived as a child.

[nhchris]

Even supposing children are raised communally by the tribe, female fertility rapidly declines post-30, and falls off a cliff post-35: https://www.britishfertilitysociety.org.uk/fei/at-what-age-d...

So you have very few fertile years left into which to fit multiple healthy children. 2.1 is needed to merely sustain a population (with all the medicine of industrialized society to keep them alive). For "wild" humans, that number would be considerably higher.

[hotpotamus]

This is the intro of Idiocracy. It's worth a watch.