For guys no limit correct, but younger males have a higher spermcount.
The female is clearly the biggest factor for your chance to conceive, but if you have a older woman + younger male it does compensate a little bit at least.

For females generally speaking untill 30 it's easy to conceive, 30-35 it's a bit harder, 35-40 it's very hard, 40-45 best chance is IVF .
Also important to note if a female was pregnant before it slows down the age factor. So if a woman has a child at 28 for example and at 44 deciddes I want another child ! it's more likely for that woman to conceive than for a first time mother. This explains why sometimes married couples have "accidental " younger children compared to the rest of their children.