We always here about women missing out on kids but plenty of men do too. This is often because men dont FEEL like they have a biological clock so they often leave it to the last minute. There is plenty of men in their late 30s, 40s and 50s just now realizing they want kids but that ship has sailed, unless they some how get lucky. If men want kids they should leave it to 35 at the latest.

Why men over 35 will struggle to have kids:

-Women in their dating pool have already had kids and dont want more.

-Women in their dating pool often have fertility issues and also might not be able to have the amount of kids that they want

-Fertile women dont want to have kids with someone much older or even be in a relationships with a man much older. Women statistically date men 2-4 years older and marriage rates among age gap relationships are a a much greater risk of divorce. So no men over 30 cant just choose some early 20s women to have kids with despite their fantasies.

-"For men, aging can affect the quality of their sperm, including the motility, morphology (shape) and concentration, which then makes it more difficult for sperm to fertilize an egg. Men also produce lower sperm counts as they get older."

"Another study of intrauterine artificial insemination found that after six cycles, men who were 35 or under had a fertility rate of 52%, whereas men over the age of 35 had a fertility rate of 25%"

So from all this I would suggest if a man actually wants kids he should start looking at around 25 for a suitable partner. Considering you probably want to be in a relationship for at least a couple of years before having kids. And then between each kid there will be at least a year gap.