Answer: Pope Leo XIII born March 02, 1810, and died July 20, 1903 at age 93, making him the longest living Pope at the time. He was also the third-longest reigning Pope (1878-1903).

However, on September 4th, 2020, Benedict XVI became the longest-lived person to have held the office of pope, at 93 years, 4 months, 16 days, surpassing Leo XIII, who died in 1903. With the death of Cardinal William Wakefield Baum in 2015, Benedict became the last man alive who was made a cardinal by Pope Paul VI.

See also:
James C. Hamilton, Notable Postcard: Pope Leo XIII Sede Vacante Vatican Notes Volume 61 Issue: 60th AV 2013 Page: 4


Pope Leo XIII
Scott # 1145 (2000)