I'm 25 years old. A couple of centuries ago, you “came of age" at 16, but industrialization and the need for educated workers instead of strong ones pushed that number to 18.
My age doesn't make me feel like an adult. "Adult" to me was my mom, my teachers, or generally people with whom I had nothing in common. They accepted me into the club years ago, but I feel like I don't belong.
You buy a car, rent an apartment, pay taxes, pay bills, hire people, pay salaries, receive checks, know what a check is and how to fill it out, clean dishes voluntarily, negotiate with people twice your age, people twice your age ask you for things, you plan a life with someone. And still, I don't feel like I am one.
My car is an expensive toy. My apartment is a base of operations. My company is a fun challenge to play with all day, not a job to support a family. Money is the points that allow you to win the game, not the end for which you work. The line separating hobbies from work doesn't exist. As XKCD says, my brain stopped growing many years ago, and I've been pretending ever since.
What does it mean to be an adult if I still feel like a child? Have a child? Support them? Get into debt? Create a family? Create a company? Another company? Travel more? Travel less and settle down?
Maybe one day they'll discover I never grew up and they'll put me under responsible adult supervision. Then perhaps I'll feel safe to continue playing, as I have done until today.