Teens and early twenties are considered the perfect age to start pumping iron. It coincides with testosterone-induced muscle growth after puberty. That was the best time, and the second best is now! There is no upper age limit. Check out Arnold and Robby Robinson at 75.With age, you naturally lose muscle strength and bone density. The remedy – bodybuilding! Apart from 1RM, the 18-40 age group (male and female) shows no significant change in muscle growth in response to the training.