There was a book a few years ago about this subject for women...it didn't sell well. 35 is really the magic number. Down Syndrome potential ratchets up massively after that, frex.
Men are not immune from it either. schizophrenia and other issues seem to correlate to older paternal age too.
The effects of older parents having kids are something that almost everyone wants to avoid talking about. Postponing having kids until after you are 30 has dangers and as more and more of us do it...
Always draw your curves, then plot your reading.