It is commonly assumed that only women have biological clocks and that men can continue to father healthy children their entire lives. Just look at Tony Randall and Rupert Murdoch, who both became dads when they were in their 70's.

Geneticists have long known that older fathers risk an increase in certain birth defects, such as dwarfism, skull and facial abnormalities and neurofibromatosis. New research shows that there may be even more risks associated with becoming a father at a late age and that maybe men should be listening to ticking of their own biological clocks.

One recent study found that men over 40 were 5.75 times more likely to father a child with autism and related disorders than a man under 30 years of age. There are also indications that men over 40 may have a higher risk of having a child with schizophrenia and certain cancers.

While many are skeptical about these findings, others see this as a long overdue wake-up call for men. "The message to men is: 'Wake up,'" said Pamela Madsen, executive director of the American Fertility Association, a U.S. education and advocacy group. "It's not just about women anymore, it's about you, too."

Health reasons aside, some feel that just because a man can have a child in his golden years, doesn't mean he should, and that older fathers should consider how their advanced age is going to affect their offspring.

In my own experience, keeping up with an active 6 year old was a lot easier in my 20's than it is now that I am over 40. I can still do it, but it takes more out of me. In 20 years, I am quite sure I won't be up to it. And what about being there for them as they grow up? Even though Tony Randall was able to father a healthy child at 77, his death in 2004 left a 7 year old without a father.