According to a news article from the BBC (http://news.bbc.co.uk/1/hi/health/7931982.stm), the older dads are, the decrease in the baby's brain power. Doesn't state what the cut off point is.
So men have biological clocks too. Who'd have thought it. When we were pregnant (it's always we, though I could swear sprog was inside me and me alone) I got many raised eyebrows and serious talks about the dangers of having a child at my age. And before you ask, I'm not THAT old.
Wish I'd known about the dangers of aging sperm before attaching myself to a 40 year old. I would have gone for a lithesome 20 something.
Having said that the tod seems to be pretty clever so maybe hubby's little swimmers aren't yet past their use by date.