I will agree with you that maturity is in the mind, it has nothing to do with one's age. When you are able to have a self awareness, you are able to process your feelings or emotions and manage conflicts, and also being able to take responsibilities of your actions then you are matured. And this maturity are in four levels; spiritual maturity, physical, emotional and mental maturity. All these helps in shaping a person's life. I enjoyed reading from you, thank you for sharing and best of luck