98 There are young persons who desire quickly to attain to old age, so as no longer to be subject to the will of their elders; and there are also old men who would wish if they could to return again to youth. And I approve of neither desire, for the young, disdainful of things present, as it were ungratefully desire a change in their way of living, the old wish for its lengthening, whereas youth can grow old in character, and old age grow green with action. For it is discipline as much as age which brings amendment of character. How much the more then ought we to raise our hopes to the kingdom of God, where will be newness of life, and where will be a change of grace not of age!
Source: Letters (New Advent)