I'm not making this shit up.
Well, it makes sense in terms of sexual competition, especially in non monogamous species to have ways to keep the semen alive longer while remaining mobile/fast to get the best ratio of survivors at 'the end of the road' and therefore more fecundity. While there's no incentive (well, more with a slow growing cultural social species such as humans but still relatively few) to hold aging in a population (in terms of natural selection).
Slowing Aging ... With Semen - Health Checkup: How to Live 100 Years - TIMEHold your laughter. It's not the setup for a joke. Austrian researchers believe that a compound in human semen can have a dramatic impact on life span. Biochemists Frank Madeo and Tobias Eisenberg at the University of Graz led a team to test the effects of a substance known as spermidine. In yeast, spermidine was shown to increase life span by as much as a factor of four; in fruit flies, up to 30%; and in worms, up to 15%. When spermidine was applied to human immune cells, they too lived longer, with three times as many surviving after 12 days as in a comparison batch.
Spermidine works, the researchers show, by promoting the cellular process of autophagy — a kind of self-cleaning that, Eisenberg says, "removes cellular garbage such as clumped proteins or damaged or defective cellular organelles." Those things might otherwise harm the body.