80) Harrison Ruffin Tyler
Surviving grandson of 10th US President John Tyler
Born: 1928
The 10th United States President had fifteen children between his two wives and died a solid sixty years before his youngest grandchildren (including Lyon Jr and Harrison) were born.
Harrison reportedly still lives at the Sherwood Forest Plantation, the historic home belonging to the Tyler Family. His father was seventy-five years old when he was born.
Sources:
https://allthatsinteresting.com/john-tyler-still-has-two-living-grandkids
https://www.cbsnews.com/news/how-two-of-president-john-tylers-grandsons-are-still-alive/