Earlier quoted context omitted.
I have a different pet explanation from the other replies here, and I honestly don't get why it's not talked about more. Basically, our economic reality and expectations have come into conflict with biology and human lifespan. If you want a secured dignified life and basic prerequisites to starting a family, every year that takes a little longer. And these days, almost everyone wants that dignified middle class life…
So support should be provided for incentivizing younger parenthood then, like guaranteed tuition assistance per children born?
I'm not sure that's enough to reverse the demographic slide though, it's been tried.
For our ancestors, they married young, and didn't have access to birth control. Babies weren't really planned, they just happened.