In honor of this coming Memorial Day, we offer this roster of those said to be the longest-lived veterans of the six major wars that the United States was involved in, through World War I. Records for the Revolutionary War are somewhat sketchily verified, so we've listed a few candidates, and there might be yet others worthy of this list, which we would be glad to hear about.
American Revolutionary War (1775-1783)
Barnabas Cochran (1758-1864), Pennsylvania Militia
Samuel Downing (1761-1867), New Hampshire Line
John Gray (1764-1868), Virginia Militia
War of 1812 (1812-1815)
Hiram Cronk (1800-1905), U.S. Army (he enlisted at age 14)
Mexican American War (1846-1848)
Owen Thomas Edgar (1831-1929), U.S. Navy
American Civil War (1861-1865)
James Albert Hard (1843-1953), Union Army (last verified combat veteran)
Pleasant Riggs Crump (1847-1951), Confederate Army
Spanish-American War (1898)
Jones Morgan (1882-1993), U.S. Army
World War I (1914-1918)
Frank Woodruff Buckles (1901-2011), U.S. Army
Sources: revolvy.com; nps.gov; bytesofhistory.org; suvcw.org; thecivilwarparlor.tumblr.com; spanamwar.com; frankbuckles.org