Why do we humans have to act mature when we are already adults?

sure. We are capable of more decision making than most animals and that includes really stupid decisions. However most people do not have a mature brain until age 21 so in general its easier to make good decisions as an adult

Some teenagers can be wiser than some adults, but it depends on the individual. I know some pretty immature adults and some pretty mature teenagers, but unfortunately you can’t generalize about who is cleverer than who.

in my opinion it is compleatly possible, it depends on what the indivudual has gone through in life. hard times in life often make us much stronger after we get oven them almost everyone can agree and relate with that but it is what we learned from it that matters and detremins how muture one is. there for I belive it is complealtly possible and likely that many teenagers are wiser than adults in some areas. Although that is most deffently not always the case