Years wrinkle the skin, but to give up enthusiasm wrinkles the soul.
Whether seventy or sixteen, there is in every being's heart the love of wonder, the sweet amazement at the 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. 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 the snows of pessimism and the ice of cynicism, then you are grown old indeed and may God have mercy on your soul.