Age and maturity have nothing to do with one another. A person's life experiences are likely to help with the maturing process. As we go through difficult situations we learn to adapt and grow. Some people go through life avoiding many of these obstacles. This is why you can meet a fifty year old woman that still gossips, drinks, and acts as if they have never gotten out of high school. Life has a different path for each of us.
Age does not divine maturity. It does not, just because some one is 16 doesn't mean they are mature enough. You don't know how mature people are. Some one could be 14 and they could be mature. Someone could be 24 and they might not be mature at all. You can't judge them by maturity just because of their age. You don't know them. You have to get to know them to figure out how mature they really are. So don't say that if some one is 16 they are not mature, because you don't know if they are or aren't. So stop saying age defines maturity cause it does not.
A person at the age of thirty could be less mature than an 18 year old from a psychological standpoint. Physically age defines maturity, but not mentally. For example, a young person could make good investment choices and have mature relationships whereas an older person may make shortsighted and selfish choices because they are less mature.