When boys are born they do not have sperm cells, but are born with the cells from which sperm cells develop. Males start to produce sperm during puberty.
Men are most fertile in their 20s. Sperm is generally healthy and plentiful. Fertility starts to gradually decline, but many men in their 30s can father children without difficulty.
Fertility decreases more noticeably when men are in their 40s, especially after the age of 45. Sperm numbers and quality can decline, affecting the chances of conceiving. After age 50, fertility drops significantly. There is a higher risk of fertility issues in older ages because the number and the quality of sperm cells decrease. Genetic and lifestyle factors, such as smoking, will influence how quickly fertility in men decreases.
Girls are born with a fixed number of eggs in their ovaries, and these are all the eggs they’ll ever have. The number and quality decrease with age.
In their 20s, women are most fertile. The eggs are the most healthy at that age and there are plenty of them. There is a high chance it will be easy to get pregnant quickly.
The quality and quantity of eggs decrease with age – fertility starts to decline after 30, then there is a sharp drop after 35. It might take longer to get pregnant, and the risk of miscarriage and genetic problems increases.
Fertility drops again even more after 40 years of age. Once the number of eggs goes down to zero which usually happens around the age of 50, it is no longer possible to get pregnant with your own eggs. Genetic and lifestyle factors, such as smoking, could influence how quickly the number and quality of eggs decrease.