Those are some grim things that you mention, that are committed by some adults. Don't worry, it is not compulsury adult behaviour to behave in such a way if you don't want to. Yes, we all have to grow up and become adults. That means taking on responsibilities for our own lives, getting jobs etc and doing stuff we don't always want to do. Take heart, though... our twenties can be a great time too, and we can still act young throughout them. I just found my twenties to be like my teens, but with more freedom. I had a job, but that was only like school but with pay. I bought a house, which though gave me a mortgage, also gave me a lot of freedom for partying. The extra money gave me the freedom to buy all the things that I couldn't afford to buy as a teen. Even our thirties are not bad. Okay, I'd got kids of my own by then, but I still did pretty much what I wanted (and at 44, I still do).
Basically, don't fear getting older... embrace it. Use it as an opportunity to do what you want to do. Like my ex-wife once said to me... "It's alright for men... They never have to grow up."