To me, being successful means...
Feeling fulfilled in a major aspect of your life, whether it is in the context of family, career, spirituality, etc. Pursuing interests. Having interests. Feeling happy with yourself and the person you are. Feeling content and at peace. Being financially comfortable and emotionally stable.

My definition of success has not changed over time. 
My definition of success really hasn't changed much over time. In high school, I may have also included more age-appropriate things like getting good grades or making my parents happy, but I always knew success was a big-picture rather than snapshot thing. I think I was always aware that true success was more of an intrinsic rather than extrinsic accomplishment.