Our usefulness is not diminished by old age,
if anything it is heightened,
because we will know God more intimately
at 80 than we did at 20.
[The righteous] still bear fruit in old age;
they are ever full of sap and green,
to declare that the Lord is upright;
He is my rock, and there is no unrighteousness in Him.
Psalm 92:14-15 ESV