Do you hear it? Tick, tick, tick ... hmmmm, perhaps it's one of two things: 60 Minutes is on TV; or maybe, just maybe, it's your biological clock ticking.

Is there really a biological clock ticking away ... for guys? While just a common metaphor, the proverbial biological clock is certainly a real phenomenon in women. Statistics from the American Society for Reproductive Medicine show that women over 35 years of age are only half as likely to become pregnant. Not so with men.

Men are Good to Go

Physiologically speaking, it's 'go time' for men virtually right up until the grim reaper taps them on the shoulder. Men produce sperm their entire lives. And there are plenty of examples of this: Silent film legend Charlie Chaplin sired a child when he was 73. Comedian and actor Tony Randall became a dad at 79. Writer and Nobel Prize-winning author Saul Bellow pushed aside his keyboard long enough to father a child when he was 84. Oh, and then there's Nanu Ram Jogi, a farmer in the Indian state of Rajasthan, who fathered his 21st child at the age of 90. And Hugh Hefner -- well, let's not even go there.

Other late parental bloomers:

David Letterman, at age 61

Donald Trump, 62

Sylvester Stallone, 62

Rod Stewart, 63

Michael Douglas, 64

Mick Jagger, 65

Paul McCartney, 66

Clint Eastwood, 66

Sir Michael John Gambon, 68

Woody Allen, 73

Larry King, 75

Anthony Quinn, 81

Risks for Older Dads

What drives a man to want to become a parent, especially after years of daddy denial? Is it hormonal? Is it a sense of mortality or a desire to pass on the family name? Or could it simply be a desire to break from meaningless trysts to find a relationship that can only be validated by having a child? All good questionsÂ…but no good answers. There is little or no research that suggests age or biological factors for men wanting to have children. Men are not born with a limited number of a few hundred thousand sperm that they must use up before the age of 45 like women do with their eggs. Men are constantly making new sperm and they have an endless supply of it too. The only problem with men's fertility is that as they age, the quality of their sperm decreases, as every cell in your body ages, so does your sperm.

There are some risk factors as men get older. A 2005 study conducted by the University of California, Los Angeles, found a fourfold rise in Down syndrome among babies born to men 50 and older. And in a 2006 study conducted by Mount Sinai School of Medicine, researchers found that fathers in their 30s have children with about 1.5 times the risk of developing autism compared with fathers in their teens and 20s. That factor jumps to five times for dads in their 40s.