Why do a lot of people always say, "Oh you can grow in your 20's." I hate that.
Some boys don't start puberty until they are 15 or 16. Since adolescence can last six to eight years, that means some boys don't finish growing until they are 21 to 23 years old. This doesn't mean that all boys continue growing into their twenties.
However, just about all boys do continue maturing into their twenties. Even after you stop growing in height there are still changes that take place, such as hair growth, muscle development, and brain development. For example, one of the last changes young men experience is the maturing of the section of the brain that analyzes decisions, weighing the risk factors. That section of the brain often doesn't finish development until a young man is in his early twenties, which is why car insurance is high until you turn 25.