Mark Twain was 23 when he became a licensed riverboat pilot.
Twain, whose real name was Samuel Clemens, received his pilot’s license on April 9, 1859. He had begun training roughly two years earlier as a “cub” pilot under Horace E. Bixby, learning the Mississippi River’s hazards and navigation routes between St. Louis and New Orleans.
The distinction between training and licensing explains why other ages sometimes appear in biographies. Clemens began his apprenticeship at about 21, but he did not receive his full license until he was 23. Once licensed, he worked as a professional pilot and earned a respected income on the river.
His river career ended when the Civil War disrupted commercial steamboat traffic in 1861. The experience nevertheless shaped his literary identity. He later drew on it extensively in Life on the Mississippi, and the riverboat expression “mark twain,” meaning two fathoms of water, became his famous pen name.