As you grow, you learn more. If you stayed as ignorant as you were at twenty-two, you'd always be twenty-two. Aging is not just decay, you know. It's growth. It's more than the negative that you're going to die, it's the positive that you understand you're going to die, and that you live a better life because of it.
Morrie speaks these words of advice to Mitch on their seventh Tuesday together, when they discuss the common fear of aging. Morrie tells Mitch that the happiness of youth is a farce, as not only do young people suffer very real miseries, but they do not have the wisdom of age to deal with them. Morrie has never feared aging; he embraces it. He believes that if he were to wish for youth, that would indicate his dissatisfaction with the life he has lived. He explains to Mitch that to fight age is fight a hopeless battle, because aging and death are inevitable, and a natural part of the life cycle. Morrie has lived through every age up to his own, and he is therefore a part of each of them. He does not wish to return to these particular ages, as each of them are constituents of the man he is now. He is more eager to explore new frontiers he must face in the future, even if that future is very limited. In accepting his own death, Morrie is able to savor the little time he has left to live, instead of wasting away, frustrated and angry that his time on earth is soon to end.