The glory of young men is their strength - Scarcely any young man affects to be wise, learned, etc.; but all delight to show their strength and to be reputed strong. Agility, one evidence of strength, their particularly affect; and hence their various trials of strength and fleetness in public exercises.
And the beauty of old men is the gray head - They no longer affect strength and agility, but they affect wisdom, experience, prudent counsels, etc., and are fond of being reputed wise, and of having respect paid to their understanding and experience.

The glory of young men is their strength,.... That is the excellent thing in them, and it is to their honour when it is employed in the service of their king and country, and especially in the service of God and religion; though it does not become them to glory in it, Jeremiah 9:23;
and the beauty of old men is the gray head; an index of wisdom and prudence; see Job 12:12. The design of the proverb is to show that both have their excellencies and usefulness, young men and old men, and should not despise one another; nor either of them be despised in a commonwealth, both being useful in it, the one for strength, the other for counsel; and so in the church of Christ; see 1-John 2:13.

Both young and old have their advantages; and let neither despise or envy the other.

The glory of young men . . . the beauty of old men--Each age has its peculiar excellence (Proverbs 16:31).

29 The ornament of young men is their strength;
And the honour of the old is grey hairs.
Youth has the name בּחוּר (different from בּחוּר, chosen), of the maturity (R. בחר, cogn. בכר, בגר, whence Mishn. בּגרוּת, manhood, in contradistinction to נערוּת) into which he enters from the bloom of boyhood; and the old man is called זקן (Arab. dhikn, as Schultens says, a mento pendulo, from the hanging chin זקן, (Arab.) dhakan, chin, beard on the chin). To stand in the fulness of fresh unwasted strength is to youth, as such, an ornament (תּפארת, cf. פּארוּר, blooming colour of the countenance); on the contrary, to the old man who has spent his strength in the duties of his office, or as it is said at Proverbs 16:31, "in the way of righteousness," grey hairs (שׂיבה, from שׂב, Arab. shâb, canescere) give an honourable appearance (הדר, from הדר, turgidum, amplum esse, vid., at Isaiah 63:1).