In fact, the biological clocks of men and women are very different. Most women know that at menopause, their eggs have decreased in quantity and quality, and age plays a huge factor in the ability to conceive. In contrast, a man produces sperm throughout his life. It is noted that between the ages of 30 and 50, there is a slight decline in fertility (including a decrease in sperm motility by 37%, an increase in the content of abnormal sperm by about 5 times/abnormal sperm shape, and a decrease in semen volume by about 30%), but the quality of a man's semen does not decrease. In this article, we will provide useful information about the differences in biological clocks between the two sexes.