“The common assumption is that it (old age) is mainly a process of loss, whereby strength is drained from both mind and body and the capacity to look forward and move forward in life’s various departments is reduced to nothing. . . .
But here the Bible breaks in, highlighting the further thought that spiritual ripeness is worth far more than material wealth in any form, and that spiritual ripeness should continue to increase as one gets older.
The Bible’s view is that aging, under God and by grace, will bring wisdom, that is, an enlarged capacity for discerning, choosing, and encouraging. In Proverbs 1-7 an evidently elderly father teaches realistic moral and spiritual wisdom to his adult but immature son. In Psalm 71 an elderly preacher who has given the best years of his life to teaching the truth about God in the face of much opposition prays as follows:
You, O LORD, are my hope,
my trust, O LORD, from my youth. . . .
Do not cast me off in the time of old age;
forsake me not when my strength is spent. . . .
But I will hope continually
and will praise you yet more and more.
My mouth will tell of your righteous acts,
of your deeds of salvation all the day,
for their number is past my knowledge.
With the mighty deeds of the Lord GOD I will come;
I will remind them of your righteousness, yours alone.
O God, from my youth you have taught me,
and I still proclaim your wondrous deeds.
So even to old age and gray hairs, O God, do not forsake me,
until I proclaim your might to another generation,
your power to all those to come. (Ps. 71:5, 9, 14-18)
And Psalm 92:12 and 14 declare:
The righteous flourish like the palm tree and grow like a cedar in Lebanon. . . .
They still bear fruit in old age;
they are ever full of sap and green.
This biblical expectation and, indeed, promise of ripeness growing and service of others continuing as we age with God is the substance of the last-lap image of our closing years, in which we finish our course. Runners in a distance race, like jockeys in a horse race, always try to keep something in reserve for a final sprint. And my contention is going to be that, so far as our bodily health allows, we should aim to be found running the last lap of the race of our Christian life, as we would say, flat out. The final sprint, so I urge, should be a sprint indeed.”
Finishing Our Course with Joy: Guidance from God for Engaging with Our Aging (Crossway, 2014) as quoted by Justin Taylor on the Gospel Coalition.