It is thought that accumulation of chromosomal aberrations and mutations during the maturation of male germ cells are responsible for increasing risks of certain conditions with advancing paternal age. The amount of DNA damage in sperm of men aged 36–57 is three times that of men <35 years. There is a recent body of literature discussing the possible effects on reproductive outcomes, which has been summarised by Kühnert and Nieschlag.
The average age of childbearing for women is also increasing, resulting in higher risks of adverse reproductive outcomes. Healthcare systems have responded to the increased risk associated with delaying maternity by offering screening for congenital abnormalities and treatment for infertility. (Source: Advanced paternal age: How old is too old?, by Isabelle Bray and David Gunnell, George Davey Smith; Aitken R J, Koopman P, Lewis S E M. Seeds of concern. Nature 200443248–52; Kühnert B, Nieschlag E. Reproductive functions of the ageing male.)
Researchers believe that the increased risk of health conditions might be due to age-related genetic mutations in older men. Despite the increase in these risks, however, the overall risks remain small and less certain than those associated with being born to a woman over age 40. (Source: "How does paternal age affect a baby's health?" by Todd B. Nippoldt, M.D. Mayo Clinic, June 19, 2015)