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93 years old. Pope Leo XIII, born Gioacchino Pecci, was the 256th pope of the Catholic Church, reigning from 1878 until his death in 1903. He was the oldest pope to be elected and the oldest to die, passing away at the age of 93. During his papacy, he issued numerous encyclicals on social and political issues, including the landmark "Rerum Novarum," which addressed the plight of the working class.