There is generally no upper limit to the maximum age at which a man can be fertile for no particular reason, but there is a gradual decline after the age of 40. Male fertility depends largely on the availability of competent sperm, which occurs continuously from puberty to old age. Sperm will still be present in the testes of men in their 80s and 90s, albeit in small numbers, and are theoretically fertile. As a man ages, his body functions decline and other factors, testosterone levels and secretion of epididymal fluid decrease, and the lack of nutrients for sperm affects sperm maturation. A man’s ability to produce sperm diminishes, so that the probability of a woman’s conception gradually decreases, and there is a significant decline after the age of 40. A man’s fertility can be maintained until a higher age, but it gradually declines with age. If you want to assess whether a man is fertile, you can go to the hospital for a routine semen test after two to seven days of abstinence to make an initial assessment by looking at the sperm count and sperm motility.