This quote means that how old or young you feel is determined by your attitude, outlook, and emotions. If you are confident in yourself, you will feel young and energetic. But if you are full of fear and despair, you will feel old and weighed down. If you have hope, you have the potential to feel like anything is possible and stay young. On the other hand, if you have feelings of hopelessness, it can drag you down, making you feel much older than you are.