The ability state of human body changes day and night. Every day from 8: 00 to 12, from 14 to 17, muscle speed, strength and endurance are in the best condition. If you do physical exercise and sports training during this time, the effect will be better. But from 3: 00 to 5: 00, 12 to 14, it is in a relatively low state. If you are engaged in sports during this time, you are easy to get tired, and when the "load" is too large, the probability of sports injury is high.
As far as health is concerned, it is effective to start exercising at any age. Exercise more when you have time, but exercise less when you have no time. Just move, even if it's just a trick.