The production of sperm cells begins later in life compared with the egg cell production.
Eggs or female reproductive cells are formed well before birth in a huge number (primordial oocytes). But, the number of oocyte decreases after birth constantly (there are 2 million oocytes at birth and 40,000 of them in puberty). At menopause, no egg cells are left.
On the other hand, the first sperms are formed only from puberty, but the production of those cells never stops.
