Male age has a much smaller impact on fertility than female age. In fact, sperm counts and motility do not necessarily decline with age alone, nor do pregnancy rates. However, age can exacerbate pre-existing fertility disorders.
Certain genetic causes of low sperm counts will cause progressive decline over time. Untreated varicoceles may degrade sperm production over time and a man who could get his partner pregnant in his younger adult years may be unable to years later due to his varicocele. The younger a man is when he corrects the varicocele, the greater the improvement tends to be. As a man ages, there will be a low level increase in genetic irregularities that accumulate in the genes of forming sperm. Although the absolute risk is very low, the risk of genetic diseases that are autosomal dominant increases by 20 percent in the offspring of men older than 50. There is suspected to be a five percent increase in heart abnormalities such as ventricular septal defects, artrial septal defects and patient ductus arteriosis. Other conditions that are suspected to be slightly increased include situs inversus, neural tube defects, Down syndrome, prostate cancer, schizophrenia, achondroplasia, congenital cataracts, leukemia and sporadic nervous system cancer.
Remember, the absolute rates of these conditions is very low to begin with and the suspected increase is a small to modest percentage of a very low number.