Male fertility declines with age. "For example, most of the public are unaware that it takes five times longer to achieve pregnancy when the father is over 45." - Quote by Annabel Slater for BioNews
It is not necessarily the quantity of sperm that declines as a man ages, yet it is the quality of the sperm that declines.
Story via BioNews (bionews.org)
IVFandFertility.com