Advanced paternal age
"Do older fathers have an increased risk of fathering children with birth defects?
No medical information exists to support the hypothesis that increased paternal age causes increased numerical chromosomal abnormalities as increased maternal age does. As males age, however, structural spermatozoa abnormalities are increased. The literature suggests that older fathers have a 20% higher risk of transmitting autosomal dominant diseases as a result of abnormal cell division. Autosomal dominant disorders include neurofibromatosis, Marfan syndrome, achondroplasia, and polycystic kidney disease. In fact, the American Society of Reproductive Medicine recommends an age limit of 50 years for semen donors.
Any family with a history of birth defects should seek individual genetic counseling. To determine whether an individual has a family history of risk, patients should inform their physician or genetic counselor about any birth defects that have occurred in the past 3 generations."
Depending on where you read it, advanced paternal age is defined as about 40 y/o, sometimes as early as 35 y/o.