When a couple has trouble conceiving, don't necessarily blame the woman and her limited supply of eggs—men's fertility starts dropping even before women's, Time reports. In addition to fecundity issues, older men also risk siring children with higher rates of autism, schizophrenia, Down syndrome and bipolar disorder. Male fertility may peak as early as age 24, researchers say.
So what's wrong with older sperm? Sluggish swimmers, or a decrease in their numbers, could contribute to the effects researchers have seen, and lowered testosterone might play a role as well. Or it may be all in the DNA: Though sperm are never much more than 90 days old, the cells that produce them are subject to ravages of time.