It looks like women aren't the only ones with a biological clock. Ours just runs a lot slower than theirs. According to this article, older fathers produce children with slightly reduced cognitive abilities:
A new study of old data on 33,000 young U.S. children finds those with older fathers had reduced cognitive abilities. The differences, however, are slight, and no study has been done to see how such children fare later in life.
"The older a dad is, the worse his children tend to do in intelligence tests," said study leader John McGrath from the University of Queensland.
The reason may involve aging sperm.
"We are concerned that older men accumulate more mutations in the developing sperm cells," McGrath said. "These mistakes then pile up and increase the risks of problems in the children, and it is possible that these mistakes will carry on into the next generation."
The study - a fresh analysis of data on births from 1959 to 1965 - adds to a growing body of work that illustrates there are increased risks to the offspring of men who father them later in life.
A study in 2006 found older men are more likely to father dwarves, due to an age-related genetic mutation in their sperm. Other studies have shown a link between older fathers and increased chances of schizophrenia and autism in the children, McGrath said. The New York Times noted that a 2005 study found children aged 16 and 17 who had older fathers scored lower on nonverbal IQ tests, but so did children of teenage fathers.
That last bit gave me pause. As the authors of the study themselves note, the difference in the results were fairly small, and it is already known that the more involved fathers are in their children's lives the better the children tend to do academically. So it could just be that older fathers have cognitively less-developed children simply by virtue of not being as involved with them as younger fathers. Teen fathers are also not known for their dotishness.