Twenty-one years have gone by since then, but they have had absolutely no effect upon my spiritual constitution; they have left not a single trace upon it; on the contrary, I seem to feel several years younger than I felt then. When a man reaches fifty, age seems to suddenly descend upon him like a black cloud. He feels immeasurably old—very much older than he is ever to feel again, I am sure. I doubt if any person ever crosses his fiftieth parallel without experiencing what I have just described. (Mark Twain, 1906)