Samuel Whittemore was eighty years of age when he became the oldest known colonial combatant in the American Revolutionary War. From Wikipedia:
Whittemore was in his fields when he spotted an approaching British relief brigade under Earl Percy, sent to assist the retreat. Whittemore loaded his musket and ambushed the British Grenadiers of the 47th Regiment of Foot from behind a nearby stone wall, killing one soldier. He then drew his dueling pistols and killed a grenadier and mortally wounded a second. By the time Whittemore had fired his third shot, a British detachment reached his position; Whittemore drew his sword and attacked. He was shot in the face, bayoneted thirteen times, and left for dead in a pool of blood. He was found alive, trying to load his musket to fight again. He was taken to Dr. Cotton Tufts of Medford, who perceived no hope for his survival. However, Whittemore lived another 18 years until dying of natural causes at the age of 98.