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.

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.