To answer the question, “What is an adult?” you can first teach your student about self-advocacy. Becoming an adult means you are now responsible for your actions and how they affect the world around you and in turn, how your surroundings affect you. You are now your own self-advocate, and you make choices based on your preferences, beliefs, and abilities—choices that will allow you to succeed in the world.
Being an adult takes maturity and experience—and certain knowledge and skills—but there’s more to it than that. You need a certain perspective as well.