Youth is not a time of life - it is a state of mind; It is a temper of the will, a quality of the imagination, a vigor of the emotions, a predominance of courage over timidity, of the appetite for adventure over love of ease. Nobody grows old by merely living a number of years; people grow old only by deserting their ideals.
Years wrinkle the skin, but to give up enthusiasm wrinkles the soul. Worry, doubt, self-distrust, fear and despair - these are the long, long years that bow the head and turn the growing spirit back to dust.
Whether seventy or sixteen, there is in every beings' heart, the love of wonder, the sweet amazement at stars and the starlike things and thoughts, the undaunted challenge of events the unfailing childlike appetite for what next, and the joy and the game of life. You are as young as your faith, as old as your doubt; as young as your self-confidence, as old as your fear, as young as your hope, as old as your despair.
So long as your heart receives messages of beauty, cheer, courage, grandeur and power from the earth, from man and from the Infinite, so long you are young. When the wires are all down and all the central place of your heart is covered with snows of pessimism and the ice of cynicism, then you are grown old indeed and may God have mercy on your soul.