Why do sperm banks limit their donors age to 40, 38 and sometimes35?

Answer 1

Advanced paternal age: A man who is age 40 years or older at the time of conception. (There is no universally accepted definition of advanced paternal age but this criterion is often used in genetic counseling.)

Advanced paternal age is associated with an increased risk of new mutations in the offspring. This risk for genetic defects does not increase dramatically at age 40, but rather increases linearly with the age of the father. The risk of genetic defects due to new dominant mutations is 4 to 5 times greater for fathers aged 45 and above than for men in their early twenties.

Answer 2

Although sperm are made every 72 days, as a male ages, the quality of sperm decreases. As with females, the risk of having a child with certain chromosomal problems increases with age. Therefore, sperm banks want to get the healthiest of sperm to sell to their clients.

Answer 3

Because sperm quality and quantity begin to decrease around that age.

Also there is some evidence that the amount of genetic defects can go up as well.