according to studies, age causes a decline in semen volume and sperm motilitytwo key factors in male fertility. Men over 35 are about half as fertile as men under 25, and on average it takes men over 40 two years to get their partner pregnant while men under 25 take just 4. share on pinterest researchers say sperm count and lifestyle factors can lead to declining sperm quality in men over the age of 50. V or more a week actually had half the sperm of men who didnt watch t. Sperm motility was best before age 25 and lowest after age 55. In fact, when comparing the number of good swimming sperm in men between the ages 30 to 35 with men over age 55, sperm motility decreased by 54. a study in infertile men showed that taking 1,000-mg vitamin c supplements twice a day for up to 2 months increased sperm motility by 92 and sperm count by more than 100. so if youve been noticing a gradual decrease in the amount that youre spurting, say, over the last 5 or 10 years, it might just be a normal, age-related decline. Features 25-year-old women on dates with desperate 37-year-old men discussing their sperm-freezing plans. why guys are spending thousands of dollars a year to produce more semen. Semen can have low-quality sperm, while men with a low volume of semen. older men lack sperm quantity and quality from the webmd archives nov. 3, 2000 -- men holding off on making a commitment to fatherhood could end up dealing with a diminished arsenal.