When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much the old man had learned in seven years.

Mark Twain (1835-1910) American writer [pseud. of Samuel Clemens]

(Spurious)

Not found in Twain's writing.  He was eleven when his father died.