I keep asking myself that one. Occasionally I'll do things that make me "more of an adult." First it was paying taxes. Then it was getting a "real job." Then the next big step was buying a house. Then came property taxes. Recently I started wearing "grown-up clothes" when I got the job at The Company.
I didn't think I could become "more of an adult" after that.
I opened a brokerage account with one of my banks. I now own stocks!
It's kinda weird to say that I am a shareholder in a company. I want to be like that crazy lady in Futurama and say "I own one share in Planet Whatchamajigger, and I want my say!"