Some women can certainly conceive well into their 40's. Many cannot after 35. Each year after ~27-30 increases the chance that you will have difficulty conceiving.

Some can't conceive at all - the odds are still good well into their 40's, and no point scaring people into rushing into having kids when there's little evidence for it.

There is plenty of evidence that younger women (<35) get pregnant more easily, have easier pregnancies, and have lower risks of complications. After 27 or so, the odds of it all going well start to decline. After 35, which is about when women would be trying for #3 or #4 if they started in their late 20s, those odds start getting worse quickly. No point lying to people, unless for some reason you want the people listening to have smaller families.

Or, you know, you don't want to scare people into making poor life choices for themselves just to make sure they don't miss their "window".

Of course, but you also don't want to tell young women they have all the time in the world to settle down. If they want multiple children, and by the time they're 25 they still haven't found a man they expect to marry, they really need to get on that.

I guess we're thinking of children along separate lines - I see it as a potential outcome of a good, stable relationship, but you're defining it as a goal, where the getting a mate is a step in the progress towards said goal. It's just a different way of defining relationships and lives.

I think having kids is a goal for a lot of people, e.g. the girl that is the subject of this thread.

>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).

You're right - downs syndrome chance does increase with age, but yeah, there's a ton of fertile years left. 25 is not nearing the end of anything.

>there's a ton of fertile years left.

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.

At age 35, there's still 84% odds over 5 years - that's still waayy in the majority of "going to have a baby".

A) 5 years is a looooong time to be trying to conceive. Trying unsuccessfully to conceive is quite stressful.

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.