Based on the currently available information, the last member of the 91st to die was Michael King, who died on 7 December 1940, in North Union Township, Fayette County, Pennsylvania. He was 93 years old when he died.
The men who (based on very imperfect information about births) were oldest when they died were George B Kulp and David Stiefel (alias Sterle), who were both 96 years old at death.