"Data are scarce on trends in paternal age, which perhaps explains why the correlation between paternal age and birth defects went undetected for so long. And, of course, "nobody likes to think that they're aging," says Dr. Fisch. "Certainly men. They were on the throne, they were the kings: 'We don't age, we stay fertile longer than women, we can have babies into our 90s....' Men live in denial."