I'm not sure what you mean by "higher risk". The risk of a woman being unable to conceive increases each year after ~27-30, depending on the study.
I'll be having my 12th kid soon. That simply doesn't happen if you wait. At the start, I had no idea that I'd want so many kids. To allow for this possibility, you must start early. Ideally you'd start before age 20.
In college? Or high school?
I think it is important to have some means of supporting a family, but that might not involve the educational path that has become our standard for the past 30 years. It only takes one good income, and paid child care is usually a terrible deal for big families, so there isn't a financial justification for paying for two expensive educations. If the degree costs time or money and wouldn't get used, why bother? Avoiding unneeded student loans is a sensible idea. The earlier you start, the larger your family can be.
The lines between college and high school are starting to blur. Dual enrollment (or equivalent) is offered in most states. This lets students take college classes early, getting credit for both high school and college. Here it can start in 6th grade. You can get a BS degree before completing high school.
The reasons to wait are legal (typically must be 16 to marry), medical (roughly similar), and the ability to find a suitable spouse. That last one is usually easier in college. It can be a challenge to get everything in order at a young age, but the payoff is huge.
More like 20. Women are safely birthing children well into their 40's nowadays. The old "safe" age limits (generally up to 40) are no longer considered to be relevant.
>She has a career, and wants to get married and start a family sometime soon. Her boyfriend is a great person to be around and she adores him, but... he doesn't want kids (and is actually freaked out by them).
There might be, there might not be. There will likely not be many years left where the woman is most easily able to conceive a child.
B) You can't tell when you're 25 whether you're going to be in that lucky group. If having children is very important to you, those odds are not great.
C) Many people want multiple children. They can't afford to wait until it's taking 5 years to conceive each child.
The point, though, is that if a woman is still just looking for a husband at 25, when she is already nearing the end of her peak fertile years, she will likely be at the end of her peak fertile years when she gets married, so it's all downhill from the get-go.