Why do people say that if teens marry, they can't have fun anymore?

My parents and teachers have told me repeatedly this and I just don't understand. What's so hard and bad about teen marriage that you can't have fun anymore? I'm really tired of hearing things like, "Don't you want to have time to grow up, be a teenager and have fun?" First of all, if there's two things my fiance and I agree on about that, it's that being a teenager sucks and "growing up" takes forever. You can't do anything. You're powerless because you have to do everything your parents tell you (which can be enough to make want to run away and never come back.). Second, who ever said married teens will have no more fun? I never saw any proof of it.