Being mature doesn't mean the person is adult. The age is not the standard to measure whether a person is mature or not. Some teenagers know their future duty and act in a mature way. The symbol of being mature is not decided by age, but the way they think.
Firstly, the mature person must have right attitude towards life. When he gets the unfair treatment, he won't be angry and give up on himself, instead, he can adjust himself and get used to the new environment. So, no matter what happens to him, nothing can frustrate him. He always finds his own way to appreciate the beauty of life.
Secondly, the mature person must be knowledgable. As he experiences so much, he has broadened his vision. When other people ask him questions, he can give his own opinion and his profound thoughts will impress others. When we talk to the mature people, we will always learn something from them.
People like to communicate with mature minds, because it helps them to grow up. Everybody can be mature if they improve themselves all the time.