In the average human ejaculate there are several hundred million live and mobile sperm. The older a man gets the fewer sperm he manages to manufacture. By the age of eighty or ninety most men are infertile, though they often have enjoyable sex lives. In a few relatively isolated communities old men appear to sire offspring with great success, a facility that appears to be associated with great longevity – as, for instance, in Georgia in the USSR and in the valley of Vilcabamba in Ecuador. I have yet to see studies of fertility in old men in these communities. The oldest man I have seen quoted as still producing live sperm is mentioned by Havelock Ellis – “the sperm secreting function has no necessary final term and may be continued to advanced old age, even in one reported case to the age of 103.” See “Physiology of Sex” by H. Ellis.