That's not such an easy question you ask there. I'm not sure whether I am an adult or not. Some say it's when you focus on reality, but living without that childish wonder I believe is hardly living at all. You could say when you're self-sufficient, but who actually is? When you think about it, everyone depends on a lot of stuff. I vastly disagree with losing virginity or turning 18, since I know many examples of being completely immature yet still fullfilling those criteria... Perhaps carving your own path, facing the consequences of your choices is a good way of defining maturity, but a lot of kids do this (especially in empoverished places), yet calling them mature for that could be a little too exaggerated. My best guess is that one could be called mature when one has and uses all the tools to look at and discover the world critically, and make up for their own what they believe is valuable to them. That way, they can walk the path of their own choosing. I don't know if that's true, but it's the best I can come up with at this point in life.
Criterium is singular, criteria is plural, fyi.