Admiral of the Navy George Dewey was on the active list until January of 1917.

also...

LIEUT. D. ROBERTSON, VETERAN, DIES AT 87; Army's Oldest Enlisted Man Served 64 Years as Hospital Steward on Governors Island. REFUSED TO BE RETIRED Secretary Taft Drew Bill Which Congress Passed, but He Continued In Active Service.

Aug 15, 1918,

David Upton