Since 1975, there has been a hard and fast rule for participating in a conclave: A voting cardinal must be under the age of 80 at the time of the death of the pope in order to enter the conclave.
While all modern conclaves have been rather speedy affairs and have begun and ended in under a week, this was not always the case. From 1600 to 1900, 18 papal elections took more than 24 days to determine a winner, and the longest – the election of Pope Benedict XV in 1740 – took more than six months.
Among the cardinal electors in the 2025 conclave, 14 of the 135 voting cardinals are 79 years old. One, Cardinal Carlos Osoro Sierra, the archbishop emeritus of Madrid, is set to turn 80 on May 16, 2025.
The opening date of the 2025 conclave has yet to be announced, but canon law states it must begin sometime between 15 and 20 days following the death of a pope. This puts the opening day somewhere between May 6 and May 11.
But what would happen if the clock strikes May 16 and there still isn't a pope? Would Cardinal Sierra be kicked out of the conclave?
As it turns out, no. He would get to stay, but only until a pope is elected.
In Ingravescentem Aetatem, the same motu proprio that set the age limit of 80 for voting cardinals and established a retirement age of 75 for bishops, Pope St. Paul VI included a line about what would happen in this very scenario.
"If, however, a cardinal completes his eightieth year after the beginning of the conclave, he continues to enjoy the right of electing the pope on that occasion," said the motu proprio.
So that answers that: A cardinal who turns 80 during conclave can continue voting in that conclave, but cannot vote in any others.
