 Not all prime ministers live to become the oldest of their time.Of the 15 deceased prime ministers, 13 eventually became the oldest of their time, while 2 did not (William Lyon Mackenzie King and Lester B. Pearson being the only exceptions).John A. Macdonald became the oldest living prime minister when he was appointed in 1867 and remained so until his death in 1891, for a record of almost 24 years.