>Common advice is "learn to be happy with what you have", but that will never work if your dream is to do something Great, for future generations to remember -- to not throw away your shot. reading about all the people who started doing interesting things only in their 30's and forward, or those who reinvented themselves at some point in their lives and went on to be famous only on their second (or third) wind.

You've mentioned fame and being remembered by others. Is your main desire to do things or to be celebrated for having done things? Which one of those scenarios appears in your mind when you fantasize about your future? The answer to this question can sometimes be the difference between a miserable life and a happy one.