Protip: Most "adults" these days are just immature shitbags. Nobody these days seems to grow up anymore. They get out into the real world and never bother to actually strive for anything more than mediocrity. Their lives continue to revolve around teen high school drama level horseshit and they think that that's ok.
It's important to continue to have fun in life, that's just fine. Hell, I'm 26 and still love gaming, going to PAX, and all those other nerdy things. I recognize the ever lasting need for play and enjoyment of life.
Unlike most everyone else though, I realized that there's more to life than just working a job I hate, dating women I don't particularly like, and basically just wasting my life. You think all those people at the bars are actually having fun? Hell no, they consider that the be all end all of their week. They "dread mondays" because they hate the jobs they have. They whine about the people that they're dating. They drown themselves in alcohol, casual sex, and just one night's worth of fun to help them get through their pitiful lives.
And that's what passes as maturity these days. People don't grow out of high school anymore, they just trade going to classes for a day to day job. They keep on living through the same ole teen drama over and over and over.
Look at all the tools in this thread that think you need to cherish your childhood because you'll never have fun in life again. Guess what, they're all wrong. I love my job, I love the woman I'm with, I love my life and I have fun every day. I made it my life's goal to actually enjoy every aspect of my life and ever since I did that, my life couldn't be better. Hell, if I compared my time as an adult to my time as a child, I'd take adulthood in a heartbeat.
Maturity doesn't mean not having fun, maturity is being responsible and doing what you need to do. Too many people think being mature means no longer enjoying life. You can be an adult and have a lot of fun in life while still being mature. I know I do.