George Lucas, Steve Martin and Rod Stewart all famously fathered children in their late sixties.But for most men, testosterone declines as they age, which can lead to decreased libido and erectile dysfunction.

dating when your biological clock is ticking-87

“There's just no consensus on when men should be considered of an advanced age reproductively,” he says.

“But the concept is certainly one that we should embrace, in that men are not immune to the effects of ageing on their reproductive system.” For men, some of these changes are treatable or avoidable.

“I took so much crap for writing that book, it was unbelievable,” he said.

“Holy cow, when it first came out, a lot of people were upset that I was debunking the machismo image of men as they age.” Yet Fisch and others say the science is clear.

Some doctors argue against the term “the male biological clock”, mostly because they don't like the metaphor.

Larry Lipshultz, a doctor of urology at Baylor College of Medicine in Houston, says the term conveys a false sense of finality.

There are the tearful or fearful advice columns about the danger of waiting too long.

There are the pop culture references: Mindy Kaling's ticking clock, Bridget Jones talking about her “sell-by date”, or Ally Mc Beal hallucinating about the dancing baby.

Another study of about 2,000 couples in the UK showed that, after controlling for a woman's age and other factors, men who were 45 and older took five times longer to conceive than those who were 25 and younger.

Data from the UK study, published in the journal Fertility and Sterility, shows how the advancing age of women and men tends to lengthen the amount of time it takes to get pregnant.

There are the news stories about companies offering egg freezing so women can focus on their careers, rather than their biological egg timers.