Testicles like to be cooler than the rest of the body

Testicles have to be at a slightly cooler temperature for normal sperm development to take place. Muscles in the scrotum can either contract  or relax, to move the testicles closer or farther away from the body and adjust the temperature.

Men produce new sperm throughout life

Unlike women, who are born with all the eggs they'll ever have, men produce new sperm throughout most of their lifetime.

It takes about 3 months for sperm to develop and mature

Sperm require approximately 74 days to mature and up to 20 additional days to become capable of fertilisation

Age – A man's hormone levels decrease with age

With increasing age, testicles do not lose the ability to produce hormones, bu hormone levels do decrease as men age.

It's not just women who have a ticking "biological clock"

There is increasing evidence that the quality and the quantity of sperm deteriorates with age. Men after the age of 40 also have more and more DNA damage in their sperm.