The youngest sergeant ever in the US Army was this old.
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12. John Clem, a drummer boy in the 22nd Michigan Volunteer Infantry during the Civil War, he was wounded in action, decorated for bravery, and was promoted to sergeant for his actions during the Battle of Chickamauga. He retired from the army in 1915 as a major general, the last Civil War veteran actively serving in the US Army, and died in 1937.
