Due to normal, age-related changes that naturally occur in a woman’s ovaries their fertility declines, as they grow older. Women are born with all the eggs that they will ever have, while men will continue to produce sperm their entire lives.
Even if a woman have over a million eggs in her ovaries at birth, only about a few hundred will actually be ovulated during a woman’s entire reproductive years. The rest will undergo atresia, which is a degenerative process that occurs regardless of a woman’s reproductive condition. Unhealthy lifestyle can even accelerate atresia and can cause early menopause. As a woman approaches menopause, their ovaries will respond less to the female hormones. Then the menstrual cycles become shorter and their ovaries eventually will cease releasing eggs.
Though menopause in men is not considered as abrupt or noticeable as in women, changes in fertility and sexual function do occur in men too. But despite these changes, men in their senior years will still be able to father a child, or impregnate a woman. The quality and quantity of their sperm production may decline, but normally it never stops until they die. Men should be able to continue produce sperm healthy, unless they suffer damage to their testes through a serious disease or injury.
Medline Plus "Menopause". Information provided by U.S. National Library of Medicine and the National Institutes of Health.
KK Ng, R Donat, L Chan, A Lalak, I Di Pierro and DJ Handelsman (2004). "Sperm output of older men". Human Reproduction, 19: 1811-1815. European Society of Human Reproduction and Embryology.