Hard to tell.
I'm 24, happily married, one daughter and another on the way. We own our house, drive a 4 door family car, have a cat, 2 budgies, and fish. I have a stable career in programming (sitting at a cubicle all day). We go to church every Sunday. We don't really party, rarely bother drinking, and get tired at 10pm.
BUT
I speed, play hockey religiously, own every video game system on the market and play games all the time, I wear a Decepticons T-shirt to work, have toys all over my cubicle, watch cartoons, doodle, and laugh at fart jokes.
So I guess I'll let you know if I ever really consider myself "grown up". 😉😀