John Gill

Cast me not off in the time of old age,.... The Lord never casts off nor casts away his people, whom he foreknew; they are near unto him; they are on his heart, and are engraven on the palms of his hands; and they shall never be removed from his heart's love, nor out of his arms, nor out of his covenant, and shall always be the objects of his care: he bears and carries them to old age, and even to hoary hairs: the Lord had been the guide of David's youth, and his trust then, Psa 71:5; and now he desires he would be the staff of his old age; at which age he was when Absalom rebelled against him; forsake me not when my strength faileth: as it does when old age comes on; then the keepers of the house tremble, and the strong men bow themselves, and especially at death, when flesh and heart fail; but God will never forsake his people, neither in youth nor in old age, neither in life nor at death.