Man and Superman "Maxims for Revolutionists" (1903). A further extension appears in Jacob M. Braude, Speaker's Encyclopedia of Stories, Quotations, and Anecdotes (1955): "Those who can, do; those who can't teach; and those who can't do anything at all, teach the teachers."
Richard Brinsley Sheridan (1833). “The Works of the Late Right Honourable Richard Brinsley Sheridan, Collected by Thomas Moore ... A New Edition ... With a Biographical Sketch”, p.177
Mark Twain (2014). “Mark Twain on Common Sense: Timeless Advice and Words of Wisdom from America's Most-Revered Humorist”, p.61, Skyhorse Publishing, Inc.
Attributed in Reader's Digest, Apr. 1934. A similar remark, attributed to an anonymous octogenarian, appears in the Washington Post, 11 Sept. 1910. See Jefferson 42