Not really. If you had to take care of a child, you would understand what things they wanted to do were reasonable and not, right? It's the same thing. When you're enough of an adult, you will see the difference against those younger.

Also, when surrounded by others, an adult will take charge, or, at least keep their hands on the reigns in case something goes wrong.

Though, I suppose if you have to ask "what is an adult" than be default, you are not one.