Yes this is just it. Some people always complained that they are not even aware of some signs of maturity and that they want to be mature. Some says their friends always complain to them that they are not matured so they want to learn how to be matured.
I can say actually no one can learn how to be matured completely but you can act matured.
Looking at this image above, you can see some signs of maturity which will help you to become matured or even make you feel matured rather.
Try to follow this signs and you will be matured more