Dont know what I want to be when I grow up?

So in our high school people are telling us we should have some idea what we want to be. All my friends already have one or two but I dont. It worrys me because I know I want a good job and I know I want something I can look foward to doing but I just dont know what. So far im the only one with no plan. I know im still young and have a few years but I really dont know what to do. I gues what im asking is it true I should have something this time? Should I have an idea? I guess its sounds stupid worrying about an idea of what I want to be but it bothers me that I seem to be the only one. Any advice out there my friends?