Why does God let us get old and weak?

A woman who was facing the difficulties of aging asked Bible teacher J. Robertson McQuilkin,
“Why does God let us get old and weak?”

McQuilkin replied,
“I think God has planned the strength and beauty of youth to be physical.
But the strength and beauty of old age is spiritual.
We gradually lose the strength and beauty that is temporary so we’ll be sure to concentrate on the strength and beauty that is forever.
And so we’ll be eager to leave the temporary, deteriorating part of us and be truly homesick for our eternal home.
If we stayed young and strong and beautiful, we might never want to leave.”