Major General John L. Clem, born 1851... retired from active duty in the US Army in 1915, at the age of 64...lived until 1937. More than 45 years on active duty, including service as drummer and Lance Sergeant, Co. C, 22nd Michigan Infantry, from 1 May 1863 to 19 September 1864, during which service (at the age of 12-14) he was wounded twice and either shot and killed
or wounded a rebel colonel, including seeing action at Chickamauga. He later served as a courier/runner, and had two horses shot out from under him, and was decorated for bravery before being discharged in 1864
at the age of 13...
He received a direct commission into the army in 1871, at the age of 20, from no less than President Grant, and rose to full colonel, graduating from the artillery school in 1875, field service during the S-A war, and was promoted brigadier and major general on the retired list. When the United States entered World War I, Clem, 65, sought permission to be activated to join the fighting in France, but President Wilson refused his request.
Given some fairly large but not impossible butterflies, he could have been elected as late as the 'teens or even early 'twenties...
Photo taken in 1922, at the age of 71.
http://www.civilwar.org/education/history/biographies/john-clem.html
Best,