In short, enjoy the blessing of strength while you have it and do not bewail it when it is gone, unless, forsooth, you believe that youth must lament the loss of infancy, or early manhood the passing of youth. Life's race-course is fixed; Nature has only a single path and that path is run but once, and to each stage of existence has been allotted its own appropriate quality; so that the weakness of childhood, the impetuosity of youth, the seriousness of middle life, the maturity of old age—each bears some of Nature's fruit, which must be garnered in its own season.

Cato Maior de Senectute – On Old Age (44 BC), section 33