Charles H. Spurgeon on Psalms 103:5

Thy youth is renewed like the eagle's. —The Scripture knows nothing of the idea that the eagle when old renews its youth. That there is nothing of this kind contained in Isa 40:31, which is commonly appealed to, but that it is rather the powerful flight of the eagle that is there referred to, "they mount up on wings like the eagle, they run and are not weary, "is evident from the parallel, fly, run, march. E.W. Hengstenberg.