The ancient people's concept of sexual love always contains a profound concept of health preservation, and "being happy but restrained" is their consistent attitude towards sexual life. As an old saying goes, "The second watch, the third watch, the fourth watch, the fifth watch, the sixth watch." Through metaphor, it vividly reflects men's grasp of the law and frequency of sexual life at different ages. This proverb means that at the age of 20, you can have a life every two hours; Men around the age of 30 are strong and can have sex every night; 40 years old, not confused. I want to be "meticulous" like counting money and live a life once every five days; When you are 50 years old, you know your destiny. Don't be brave. You should live once on the first and fifteenth day of the first lunar month, that is, keep the frequency once every half month. At the age of 60, men should focus on keeping healthy. At this time, sex life should be like New Year's greetings, and it is appropriate to have sex once a year.