If it is muscle shaping, 20-30 years old is the most effective, because the bones are fully developed, the physical strength recovers quickly, and the androgen secretion is strong. These are all necessary conditions for building a muscle.

If you are doing aerobic exercise to increase heart and lung function and enhance endurance, then there is no age limit, just pay attention to choosing the method and frequency that suits you, don't be greedy and don't get hurt.