Matsukata Masayoshi
Not all prime ministers live to become the oldest of their time. Of the 54 deceased prime ministers, 18 eventually became the oldest of their time, while 36 did not (including all 5 prime ministers who died in office and 31 others). Matsukata Masayoshi became the oldest living prime minister when he was appointed in 1891 and remained so until his death in 1924, for a record 33 years and 55 days. Keisuke Okada became the oldest living prime minister after the death of Hiranuma Kiichirō, but he survived Kiichirō by only 46 days.