YOur brain is actually still growing until you are around 25 years old. Before that, it's natural for people to try things out thatthey haven't done before. Sometimes that goes well, and other times it is a disaster. Often, they do not understand all the possibilities if they do something, and that's when bad things happen. It's a matter of brain maturity and experience- but without the brain development, none of the experimentation will result in someone being any wiser.
Ultimately, teens are supposed to be a little wild, and try things out. That is why you are generally not put in charge of anything that can do much until later. That's why the drinking age is 21.