Successful lives, Motivation

To everyone who considers themselves to be successful in life, what are your personal little secrets that have helped you get to where you are? What did you use for motivation? I want answers that cover many areas such as weightloss, careers, schooling, taking risks, living your life to the fullest, etc.

I'm 18 and having a serious mid-life crisis, even though 18 is no where near mid-life! I'm so unmotivated, irresponsable, lost, out of control. I know what I want, I just don't know how to get it. I am very afraid that I am going to be stuck in this teenage mind set for the rest of my life, since I am so scared of growing up and growing old. Up untill now I have refused to show much sign of maturity because I want to be a teenager forever. I have realized that acting in this childish manner did not stop me from aging like I had hoped, and now I just look silly.

I do realize that I am still young, but I seriously need to get control of certain things in my life since I am no longer 15, so anything that anyone has to say would be very helpful.