You guys are complicating things too much. It's simple. The meaning of life is to have fun. You do whatever you have to do so that in the end you'll end up having fun. All the things Vox mentioned, growing up, going to school, and to college, getting a job, getting married etc. are all either conditions or ways of having fun. You need a job so you can get money and spend it on things that will make you have fun. While working might not always be fun, while it can be fun on some occasions, the money you recieve because of working makes you have fun, along with surviving to be able to have fun. I do the weirdest things with my friends sometimes, we're rather adventuristic, but it's all because we're bored and want to have fun, or in other words, just want to enjoy life. Hanging out at graveyards at night or exploring underground tunnels is all pretty scary at times, but it's fun at the same time. Playing PC Games is fun. Playing my guitar is fun and enjoyable. So that's basically it; first fill out your conditions for having fun, and then have fun until you die.
I might sound like a little kid that is never serious and just wants to **** around, but I assure you that's not true. I can be serious, I'm not immature either, I just try to spend most of my time doing things that I like and that are fun to me.