second childhood

— King David being in his childhood, an old man, in his second childhood, for all old men are twice children, as the proverb is, Senex bis puer.

— For myself, although at the commencement of the voyage I had been in bad health, and was at all times of a delicate constitution, I suffered less than any of us, being much less reduced in frame, and retaining my powers of mind in a surprising degree, while the rest were completely prostrated in intellect, and seemed to be brought to a species of second childhood, generally simpering in their expressions, with idiotic smiles, and uttering the most absurd platitudes.