Omit "if." Literally, "it (i. e., the hoary head) is found in the way of righteousness," comes as the reward of righteousness.

The hoary head is a crown of glory - The latter part of the verse is very well added, for many a sinner has a hoary head.

The hoary head [is] a crown of glory, [if] it is found in the way of (o) righteousness.
(o) That is, when it is joined with virtue, or else the older that the wicked are, the more they are to be abhorred.

The hoary head is a crown of glory,.... Gray hairs, white locks through age are very ornamental; look very beautiful, bespeak gravity, wisdom, and prudence, and command reverence and respect; with the ancient Romans (s), greater honour was paid to age than to family or wealth; and the elder were revered by the younger next to God, and in the stead of parents; See Gill on Leviticus 19:32;
if it be found in the way of righteousness; that is, if such who are old and stricken in years are like Zacharias and Elisabeth, walking in all the commandments and ordinances of the Lord blameless; when they are found in Christ, having on his righteousness; and when they live soberly, righteously, and godly; when they walk in the ways of God and true religion; keep up family worship, and private devotion; as well as constantly attend the ministry of the word and ordinances; then are they very venerable and respectable; their old age is a good old age; and in a short time they shall have the crown of glory which fadeth not away: but otherwise a sinner a hundred years old shall be accursed; an old man in the open ways of sin and vice, laden with iniquity, is a very contemptible and shocking sight.
(s) Vid. A. Gell. Noct. Attic. l. 2. c. 15.

Old people especially should be found in the way of religion and godliness.

(Compare Proverbs 20:29).
if--or, which may be supplied properly, or without it the sense is as in Proverbs 3:16; Proverbs 4:10, that piety is blessed with long life.

31 A bright diadem is a hoary head,
In the way of righteousness it is found -
namely, this bright diadem, this beautiful crown (Proverbs 4:8), which silver hair is to him who has it as the result of his advanced age (Proverbs 20:29), for "thou shalt rise up before the hoary head," Leviticus 19:32; and the contrast of an early death is to die in a good old age, Genesis 15:15, etc., but a long life is on one side a self-consequence, and on another the promised reward of a course of conduct regulated by God's will, God's law, and by the rule of love to God and love to one's neighbour. From the N.T. standpoint that is also so far true, as in all the world there is no better established means of prolonging life than the avoidance of evil; but the clause corresponding to the O.T. standpoint, that evil punishes itself by a premature death, and that good is rewarded by long life, has indeed many exceptions arising from the facts of experience against it, for we see even the godless in their life of sin attaining to an advanced old age, and in view of the veiled future it appears only as a one-sided truth, so that the words, Wisd. 4:9, "discretion is to man the right grey hairs, and an unstained life is the right old age," which is mediated by life experiences, such as Isaiah 57:1., stand opposed to the above proverb as its reversed side. That old Solomonic proverb is, however, true, for it is not subverted; and, in contrast to self-destroying vice and wickedness; calling forth the judgment of God, it is and remains true, that whoever would reach an honoured old age, attains to it in the way of a righteous life and conduct.