Problem is that the odds of serious defects rises rapidly with age. Are you ready to deal with a Down’s Syndrome kid - not just at 40, but continuing to at 50 or 60? Don’t get me wrong, it’s just an objective look at the statistics & consequences.
I used to live in NY; most all kids were normal/healthy (generally speaking).
I moved to GA; now I see what the REAL birth-defect statistics are, when the local culture doesn’t abort them. They are loved; nonetheless, they are a heavy load to bear - consider whether the two of you can handle such special needs, as some people can’t.
A friend had 15 kids, AFAIK all “healthy”, running late into her 40s. Yes, you can have healthy kids past 38. Just be aware that the odds of problems rise substantially with age, and that if you’re going to make a kid please ensure you’re healthy enough _yourself_ to in turn gestate a healthy child, and healthy enough to cope (for decades) with problems should they occur.
And for an "objective looks" at the chances for Downs according to maternal age, even the chart I posted is like something out of "How To Lie With Statistics," since it visually makes that very low 4% risk look "high." Instead of displaying it like this

It would have been more visually accurate to display it like this:

I recommend this 2-minute video, which was censored by the government --- literally banned from broadcast distribution--- in France.