According to research published in Maturitas, a European Medical Journal, men have to be as concerned about age when family planning as women do.

When they looked at pregnancies involving older men, 35-45+  the research noted a higher risk of premature birth, stillbirth, low birth weight, newborn seizures, and birth defects. They also noted  as those children aged, they also showed a higher risk of childhood cancers, mental health problems, cognitive disorders, and autism.

Several factors come into play but most relevant appears to be quality of sperm as guys get older. As sperm stem cells split and create new cells some of the DNA can get corrupted during this process, which can cause mutations, which contribute to the higher percentage rates with these issues.

Some experts recommend storing your healthy sperm in sperm banks before you reach 35 to ensure the swimmers are at peak performance whenever you may need them.