Actually, that's one of the things they found. People with degrees tend to have kids at an older age.
Logically speaking yes.
Graduate HS at 17/18
+4 years college is 21/22
Get a few years into your career and you're already across the 25 line (where Auto Insurance cuts in half, and you can afford a house on your salary)
Heck, for some people along that track, it's hard enough to even meet people to get to the point of starting a family.
For anybody on that track, having kids would seriously impair it. It is tactically best to avoid them until you're past college and in your first job decently.
For those not on that track, having kids early means being done with them by the time you're 40 or so. That's a nice perk. it also means being alive to see your grandkids (and possibly great grandkids).
One lament from a respected HS teacher I heard was that his dad had him late in life and didn't live to see his grand kid. In turn, this teacher died while his own son was in HS because he too didn't start a family until late in life.
In more personal and serious terms, my wife and I have spent the last year and considerable money to start a family, as we weren't interested in having kids until now. At 38/40 respectively, that delay has cost at least a third of my retirement fund, and if our current IVF is successful, I'll be 58 when the kid graduates HS. As my parents didn't cross the 60 line, you can imagine that we're cutting things close.
Unfortunately for women, stuff changes in their body after 30, and while waiting may be a decent economic decision initially, waiting too long creates new risks and expense. My wallet and I would have loved it if "just keep trying" was a viable option.
So, from my own experience, I expect people on the education track to wait. But they probably need to be cranking out any kids they want before 30 to avoid biological complications. Thats probably tough for some people (like me) who either don't know what they want, not in a position to get it, or change their mind later in life.