Aristotle, Rhetoric
J. H. Freese, Ed.

14. It is evident that the character of those in the prime of life will be the mean between that of the other two, if the excess in each case be removed. At this age, men are neither over-confident, which would show rashness, nor too fearful, but preserving a right attitude in regard to both, [2] neither trusting nor distrusting all, but judging rather in accordance with actual facts. Their rule of conduct is neither the noble nor the useful alone,
but both at once. They are neither parsimonious nor prodigal, but preserve the due mean. [3] It is the same in regard to passion and desire. Their self-control is combined with courage and their courage with self-control, whereas in the young and old these qualities are found separately; for the young are courageous but without self-control, the old are self-controlled but cowardly. Speaking generally, all the advantages that youth and old age possess separately, those in the prime of life possess combined; and all cases of excess or defect in the other two are replaced by due moderation and fitness. [4] The body is most fully developed from thirty to thirty-five years of age, the mind at about forty-nine. Let this suffice for youth, old age, and the prime of life, and the characters which belong to each.