Calling ID?

Recently I began to think about my calling in life. How exactly am I supposed to know what I want to be when I grow up. Granted, I am an adult but theortically I am not even middle aged so that makes me somewhat child like... right? My point is that my husband enlisted at the age of 17 and really enjoys what he does. He doesnt question it and says that he does it because its the right thing to do. It is truly his calling in life to come to the aid of others and he is willing to die for it. I spent 9 years in college trying to figure out what I wanted to do with my life and came out with 3 college degrees, people call me Dr., and I know that I want to make the world a better place. But, in reality what I really want to know is how do people know when they have found it. Found that thing that makes them who they are. At the end of the day, if I have helped one person feel good about themselves I know that I have done the world a service. I can feel good about myself if I have repaid to the world what I have taken from it but, I would love to find that thing that feeling that makes me bounce of out bed in the morning knowing I have truly made a difference. They say that Marines dont have that problem.