"You have a decline in hormones, a decline in fertility, as women age and an increased chance of genetic abnormalities to the babies born from older women. Well, surprise, that's exactly what happens to men," says Dr. Harry Fisch, author of "The Male Biological Clock."
In fact, a man's fertility begins to decline in his 30s, then steadily drops through his 40s and 50s.
A woman is born with all the eggs she will ever have. But a man produces 100 million sperm each day through cell division. The more often a cell divides, the more likely a glitch will occur as genes are copied. With billions of sperm cells dividing over a man's lifetime, that's a lot of opportunities for error.
"We've known about a lot of problems for aging fathers, but it turns out the most common ones would be those related to behavioral disorders," says Dr. Dolores Malaspina of New York University Medical Center. "So schizophrenia, autism, mental retardation and some cases of Alzheimer's have all been linked to paternal age."
But, says Jim Katchko, "You don't plan to have children later in life, it just works out that way."
Katchko was 42 when his first child, John, was born. At age 3, John was diagnosed with autism.
The children of 40-year-old dads may have double the chance of schizophrenia compared to babies born to dads in their early 20s. The occurrence of autism is about five times greater for fathers in their 40s compared with dads younger than 30.
"If I, as an older father, am contributing or could be contributing to the likelihood that he is autistic, then we need to know that," Katchko says.
While there's no proof that advanced paternal age causes autism, researchers believe the children of older dads should be screened.
"There is a lot of evidence that early interventions can really improve the long-term outcome of people with schizophrenia or autism disorders," Malaspina says.
When John was diagnosed, the Katchkos enrolled him in a special program, and now he's thriving in first grade.
"Older fathers are very valuable to the love and nurturing of a child. Some evidence shows that may offset any risk of paternal age," Malaspina says.