When someonebecomes an adult, they reach an age when they are no longer a child.Grow upis also used, especially when talking about a time in the future when someone will be an adult.
He was a young man on the verge of becoming an adult.
What do you want to be when you grow up?
Grow upcan also mean to act more like an adult in your behaviour.
Stop complaining and grow up!
The verbmaturemeans to become fully grown physically.Maturecan also be used to say that someone becomes more developed mentally and emotionally.
Some adolescents mature earlier than others.
Freddie has matured into a responsible adult.