” In essence, as men age, they experience a decrease in hormone levels which of course affect everything from sperm production, quantity, and quality to sexual drive. Although the greatest impact is seen over age 40, they experience a continuous decline throughout the lifetime. What is interesting, though, is that supplementing testosterone did not improve sperm function in one study of men who were experiencing infertility. (This may explain why making a male hormonal birth control is challenging as their system just doesn’t respond in the expected way, but that’s a digression.) However, much like the statistics for women, the majority of men are still fertile after age 40. It may simply take longer to achieve a pregnancy. “
Women go downhill after ~30 in quality, for men it seems to be ~40 for the healthiest possible offspring.
“You may have also heard that birth outcomes are not as hot for the older dad set and this was confirmed in a 2013 review in The Journal of Family Planning and Reproductive Health Care which showed that autism, schizophrenia, bipolar, and stillbirth are more common amongst children of older fathers. Before you panic, the overall risk of any of these conditions is still extremely low. Low enough that the researchers questioned if the actual risk of these outcomes outweighed the emotional and social benefits of having fathers who were more mature and established in life. “