Time to change

I am about to graduate this semester and I hate the feeling like it is time to change. I don't mind change but I keep thinking of the future. I am at that age where things have to start happening. I have to get a full time job and take care of myself. I need to get married and start thinking about a family, a house, bills, and just new things. I don't mind this but why does it have to be a certain age and time to change. Why do people always feel that because you finish college you have to change into this adult who doesn't have fun anymore. I know that is not what it means but that is what people make it seem to be. I don't want to feel like I am going to change into some person that I don't like. I want to still have fun and live life.