Generally speaking, sexual function will gradually decline after the age of 40. However, it varies from person to person, and there are some differences according to the individual’s physical condition. There is no clear standard to measure how old a man will be when his sexual function decreases. Some basic diseases or serious brain injury may cause sexual function to decrease. After the age of 40, the sex hormones secreted by the body will decline significantly, and the absence of sex hormone stimulation will lead to a decline in sexual function. If there are some serious underlying diseases, such as high blood pressure, diabetes, it will make men’s sexual function decline, when men have some serious brain lesions, such as cerebral hemorrhage or cerebral infarction, it will also make men’s sexual function decline. Men should abstain from sex in their daily life, and increase the time of physical exercise in moderation, so as to slow down the decline of sexual function through these living habits.