April 1849 - September 20, 1862: Age 13
At 13, Charlie King was the youngest official military casualty of the US Civil War. It was not unusual to have very young "drummer boys" in both armies: the very youngest combatant appears to have been a nine-year-old kid named Johnny Clem, although Clem was too young to be officially a soldier.* King, however, was old enough to be on the army payroll.
Generally youngsters were kept behind the battle lines, helping out with the wounded and making themselves useful wherever they could. His commanding officer, Capt. Benjamin Sweeney, had convinced King's father that he would keep him out of danger. However during the battle of Antietam, the boy was wounded by an artillery shell that made it over the lines. King, "shot through the body", was carried back to a field hospital, where it took him three painful days to die.
*Johnny Clem survived the war and lived to be 85.
Sources: From the Picket Line, Find-a-Grave