When Pope Benedict XVI, 85, announced his resignation, he said that “both strength of mind and body are necessary” to carry out the papal ministry in the modern world.

He was elected in 2005, just after his 78th birthday.

Of the 102 popes whose exact age at election is known, Pope Benedict was one of 17 churchmen elected bishop of Rome while between the ages of 71 and 80.

Ambrogio Piazzoni, vice prefect of the Vatican Library and author of a book on the history of papal elections, said three popes were elected under the age of 25.

The last was Pope Gregory V, who was 24 when elected in 996; seven were between 25 and 40 years old.

The last was Pope Leo X, who was 37 in 1513.