Albert Barnes Commentary Psalms 119:100

"I understand more than the aged, Because I have kept thy precepts." — Psalms 119:100 (ASV)

I understand more than the ancients — in Hebrew, "the old men." This does not refer, as the word “ancients” does in our common understanding, to people of former times, but to aged men. They have treasured up wisdom; they have had the advantage of experience, of study, and of observation.

Therefore, like teachers, they become a standard by which we measure our own attainments, as the boy hardly hopes to gain that amount of knowledge which he observes in people who are venerable in years, and who are remarkable for their acquirements. Compare Job 12:12: With the ancient is wisdom, and in length of days understanding. Consider also Job 32:7: I said, Days should speak, and multitude of years should teach wisdom. Compare 1 Kings 4:30–31.

Yet the psalmist says that he had reached this point, and had even gone beyond what he had once thought he could never attain.

Because I keep thy precepts — this is all the result of an honest endeavor to do right; to observe law; to keep the commands of God. Obedience to the law of God will do more than any mere human teaching to make a person truly wise.