OP, you've touched on something I've thought about often as I've got older.
It seems totally crazy that women are expected to somehow slot in having children in the sliver of time between establishing a career post-uni and starting to run into problems with conception. (Yes, I know that many women can conceive at 40-43, but not everyone can, and you don't know which group you're in.) This is especially true if you want more than one child.
The whole rhythm of uni to marriage-and-career to childbearing does not fit in with women's biology whatsoever. Much like the 9-5, these social norms are NOT created with women in mind. I suppose that back when women were fighting to get out of the kitchen and into the office, we just needed to prove to men that we could do the same as they did. It probably would have been a step way too far to try to join the workforce in ways that accommodate our biology.
Anyway, you're definitely on to something, OP. I have felt for a long time how unfair it is to women today that we're expected to get a higher education, marry, have a few years of marriage and building a career and THEN, when everything else is in place, try for children. It might be a good idea financially, but not so much biologically.
No wonder the birth rate is so low. Our society is not set up for women to have children. Much is demanded of us before we get to that stage; marriage is an unstable institution these days; and governments have allowed the cost of living and house prices to rise out of control with no salve, such as rent control.
Women need to feel somewhat safe and free of heavy worries like housing or relationship woes in order to have children, and I never did. Men don't want to commit and have families at younger ages, either. (Many of them think they're Adonis and as many women as possible must benefit from their golden penis before they eventually settle down. 🙄)
For me, I had an unstable marriage, and then my mum became terminally unwell, and I just became more and more tired and beset by worries, although I was still thinking of babies until I was about 41.
There's something to be said for having babies in the first half of your twenties, before the heavier things of later life overwhelm you.
I wish it was the norm for women to have children between uni and starting a career. Of course, that depends on having the right partner, I know. But being a family man is not valued in our society, so men don't want to settle down at 25.
I don't know what the answer is. I only know that society has failed in creating good conditions for women to have children in their earlier years.
Of course, there are many advantages to having children later. But I feel that many women are pushed into it being later when they'd rather have had them earlier. As it turned out, my uni boyfriend wasn't the right person for me, but if he had been, and he'd wanted the same as me, I'd have married him out of uni and tried for a family a year later. I'd have had two and then started my career in my late twenties. The IDEAL time to have kids is after uni. So much energy, few worries. (For most; I know that some deal with sick parents and other issues much earlier in life.)