Youth means a temperamental predominance of courage over timidity of the appetite, for adventure over the love of ease. This often exists in a man of 60 than a boy of 20.
Nobody grows old by a number of years.
We grow old be deserting our ideals. Years may wrinkle the skin, but to give up enthusiasm wrinkles the soul. Whether 60 or 16, there is in every human being's heart the lure of wonder, the unfailing childlike appetite of what's next and the joy of the game of living. When the aerials are down, and your spirit is covered with with snows of cynicism and the ice of pessimism, then you are grown old, even at 20, but as long as your aerials are up, to catch waves of optimism, there is hope you may die young at 80. There is no try.