Charles at Dustbury posts a Yahoo! Answers question -- the latest in a series of Y!A questions he has posted over the years that make one want to weep for the future.
When do you become an adult? This is a topic for my University essay and i want to know the answer from that point of view?
You’re an adult when you have the experience and informal learning to be able to answer the question without asking other people.
That question, and questions like it, yes. But being an adult also means still being willing to ask other people for information when your life experience hasn't encompassed it. Math questions from high-school algebra on, for example, I'm better off asking someone who's mastered it than WAG-ing it like I often did in high school.
Self-reliance within your limits is part of being an adult.
Knowing and admitting your limits is another.
Delayed self-gratification and all that other stuff too.
Oh, and knowing that no matter how much you know, or how much you can rely on yourself, there's always something you can add to the toolset. Death begins when learning ends, so stay alive as long as you can.