Let us consider that youth is of no long duration, and that in mature age, when the enchantments of fancy shall cease, and phantoms of delight dance no more about us, we shall have no comforts but the esteem of wise men and the means of doing good.
 Samuel Johnson, The History of Rasselas, Prince of Abissinia (1759). copy citation

Context

“The first years of man must make provision for the last. He that never thinks, never can be wise. Perpetual levity must end in ignorance; and intemperance, though it may fire the spirits for an hour, will make life short or miserable. Let us consider that youth is of no long duration, and that in mature age, when the enchantments of fancy shall cease, and phantoms of delight dance no more about us, we shall have no comforts but the esteem of wise men and the means of doing good. Let us therefore stop while to stop is in our power: let us live as men who are some time to grow old, and to whom it will be the most dreadful of all evils to count their past years by follies, and to be reminded of their former luxuriance of health only by the maladies which riot has produced. ”” source