Maturity cannot be decided en masse without forsaking equality. However, this is a case when equality ought to be decided on a case-by-case basis, forsaking equality for equity and fairnesss.
If a minor wishes to be granted the autonomy of emancipation and is deemed sufficiently mature, then they ought to have it granted by all rights.
If the adolescent is proven responsible, and the ability to live on their own, or with a friend/peer, they should be allowed to get out of perhaps the "sticky situation" they may be in at home. If adolescents were allowed emancipation, they may be given a sense of responsibility and reality.
From my experience, even many kids over 18 are too immature to live on their own. They fail to realize all the responsibility it takes. Sure, being an adult sounds great because you think you can do as you please. Go where you want, buy what you want, do what you want. Problem is, it's not so simple. To have these choices means you have to earn income to pay for them. That means going to the same place, every day, doing what other people want you to do. Eventually you make it back home and if your lucky, you have a bit of money left over after paying bills. Thing is, you can't even go out to spend it because you have to save it for other reasons. Doesn't really matter tho because your so tired and need to get to be early so you can do the same thing again tomorrow. Other than that, it's a blast.
Even if the kid is mature, it still wouldn't matter. Kids can't hold down a full time job and attend school at the same time. Either their grades would suffer and they would be held back, their work would suffer and they may get fired, or both. If they are in a bad situation at home, there are agencies that can place them in temporary care until they are of age.
If children under age 16 are autonomous, then they can do whatever they want. They can be employed, commit crimes, and do other things that adults can. There are many parents these days, so-called "free-range parents", who barely raise their children. If the world allowed this, parents would coerce their children into starting their own life, so they wouldn't have to take care of them. Some children would go on crime sprees, because they play too many crime-based violent video games, such as GTA (Not military games, such as CS-GO or COD). They wouldn't get proper sentences, because they're children. Child labor is a terrible thing, as children can't get their own education, and work in terrible conditions. Most children will be poor, as they don't have a good education.