Contradiction with Isaiah 46:4
While Psalms 71:9 speaks of being cast off in old age, Isaiah 46:4 assures that even to old age, God will support and carry you.
Isaiah 46:4: And [even] to [your] old age I [am] he; and [even] to hoar hairs will I carry [you]: I have made, and I will bear; even I will carry, and will deliver [you].
Contradiction with Proverbs 16:31
Psalms 71:9 expresses concern about being cast away in old age, whereas Proverbs 16:31 reveres gray hair as a crown of glory, suggesting honor and respect for the elderly.
Proverbs 16:31: The hoary head [is] a crown of glory, [if] it be found in the way of righteousness.
Contradiction with Isaiah 40:31
Where Psalms 71:9 worries about losing strength in old age, Isaiah 40:31 promises that those who hope in the Lord will renew their strength and not grow weary.
Isaiah 40:31: But they that wait upon the LORD shall renew [their] strength; they shall mount up with wings as eagles; they shall run, and not be weary; [and] they shall walk, and not faint. [renew: Heb. change]
Contradiction with 2 Corinthians 4:16
Contradicting the fear of being forsaken in old age, this verse assures believers that the inner self is being renewed day by day, regardless of outer aging.
2 Corinthians 4:16: For which cause we faint not; but though our outward man perish, yet the inward [man] is renewed day by day.