Our masters voice speaks and Asks the ScienceBloggers:
Why do men have a longer period of fertility, relative to their lifespan, than women? (Bonus: is this true of other species as well?)...
I Am Not A Biologist, but... I am a theorist, so here goes:
Because it is metabolically cheap for men to remain fertile, so worth the risk and low odds of reproductive success, particularly with possible rise in social stature at late age (and hence new mating opportunities).
Conversely, fertility is very expensive metabolically for women, and the risk high enough that at some point you're better off, in terms of genetic fitness, to be an alive grandmother or aunt, than to be the dead mother of an infant.
I don't know to what extent this is true for other species, should depend both on their social structure and reproductive strategy.
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Females of species that have "K-type" reproductive strategies, which more or less means caring for your young for a given period of time past conception - and usually, birth as well - tend to exhibit more pronounced fecundity. Fecundity is a female's ability to not only birth but also care for healthy offspring to some threshold of maturation. (That may be why curves are sexy; they advertise fecundity.) Where conversly in r-type, or, for the sake of brevity, salmon- or frog-style strategies, the majority of females' metabolic committment to reprodictive resource use is geared towards production of healthy eggs, K-types also have to be able to care for and wean their offspring. Mammals like us also have to carry the child to term etc.
Most males, however (and typically), are simply walking gamete banks, so their metabolic commitment is far lower. A K-type male could be (and often is) a deadbeat, genetically or otherwise.
I'd tend to think that it's also simply more metabolically stressful to maintain a working uterus and ovaries than a couple of testes. One of the reasons Down Syndrome spikes in women who are over forty is because the uterus can no longer screen out genetically defective embryos.
On the other hand, if a male's much metabolically cheaper sperm can make it to the egg, its work is done. The male can die immediately.
Which is why matriarchal goddess-worship makes more sense. :)
Although off topic, I'm compelled to correct a common misconception in the previous comment.
It is currently unknown why Down Syndrome risk increases as the age of the mother increases, and it is NOT due to the failure of the uterus to "screen out genetically defective embryos." The uterus does not have this capability, ever. Indeed, the risk of Down syndrome at birth *decreases* relative to the risk at 11 weeks post-conception for mothers at all ages, meaning that embryos in mothers of all ages have the opportunity and ability to abort if they can no longer grow with this defect. Embryos with genetic defects do so under their own control, there is no uterine input.
In fact, increased risk of Down Syndrome in older mothers is speculated to do with the amount of time the egg spends arrested in meiosis II (any biology book will explain this concept) before traveling down the Fallopian tube to meet with the sperm.