The study, done by researchers in Iceland, indicates that as many as 20-30% of cases of autism and schizophrenia may be linked to the father's advanced age. Unlike findings on disorders such as Down Syndrome, this study found that the age of the mother made no difference.
"This is really a paradigm shift," said Dr. Jamie Grifo, program director of the New York University Fertility Center.
Traditionally, women have borne the brunt of concerns about having a healthy child as they age, while many men have assumed their sperm were no different at 80 than at 20.
"I had my babies at 38 and 39 and I was terrified," said anchor Ashleigh Banfield on CNN Newsroom. "Honey, you're in the conversation now. It's not just me."
While older men have an increased risk of fathering a child with autism, the risk is still low -- 2% at the most for dads over 40, according to the new study.
The authors looked at random mutations in genes that are linked to autism and schizophrenia. Looking at 78 families, the researchers found that on average, a child born to a 20-year-old father had 25 random mutations that could be traced to the father's genes. Children born to 40-year-old fathers had 65 mutations.
As men age, "Sperm will have acquired more mutations than when they were younger, which will increase the chance of children they father inheriting a disease-producing mutation," said Richard Sharpe, who does research on male reproductive health at the MRC Centre for Reproductive Health at the University of Edinburgh.
One scientist said men might want to take a tip from some young women who freeze their eggs to use when they're older.
"Collecting the sperm of young adult men and cold-storing for later use could be a wise individual decision," wrote Alexey Kondrashov, a professor who studies evolution at the University of Michigan's Life Sciences Institute.