Cardinal Electors

The Cardinal Electors are those members of the College of Cardinals who have not reached their 80th Birthday on the day a "Vacancy of the Apostolic See" occurs, whether by the death or the resignation of the Supreme Pontiff. That is, if they turn 80 years of age on or before the day a Pope dies or resigns, they are ineligible to vote in the Conclave to elect his successor. However, if they turn 80 years of age the day after the Pope dies or resigns, they are eligible to enter the Conclave and vote. Interestingly, even if a Cardinal cannot vote he can be elected.

The Cardinal Electors of the Holy Roman Church

As of Sunday, May 19, 2013, there are 206 Cardinals,
114 of whom are eligible to vote and 92 of whom are ineligible.

In the Conclave of April 2005, 115 Cardinals voted.
Joseph Cardinal Ratzinger was elected Supreme Pontiff on the 4th ballot.