Leo XIII was elected on February 20, 1878.
He was elected in 2005 as pope on the 4th ballot of the conclave.
Pope Gregory VII was elected pope on April 23, 1073.
Pope Leo IX was pope until April 19 of that year when he died. The next pope was not elected until the following year.
Popes are elected for life unless they should resign. Therefore, a pope is not elected every year, only when a pope dies or resigns. The current pope (2013) is Pope Francis. He replaced Pope Benedict XVI who resigned after being pope since April of 2005.
Pope Valentine (Valentinus) was the 100th pope and ruled for one month in the year 827.
Pope Celestine III died on January 8th of that year and was succeeded by Pope Innocent III that same day.
He was elected on March 2, 1939.
The 111th pope was Pope Stephen VI who reigned from 885 until 891.
He was elected in the year 2005.
Yes, in the year 1026, Romanus, brother of Pope Benedict VIII, was elected pope upon the death of Benedict. Romanus was a layman, and essentially paid a large sum to get elected.
Pope John Paul died on April 2, 2005, and Pope Benedict was elected on April 19, 2005.
No, there is no age requirement. The only requirements are that the pope be male and Catholic. Should he not be ordained yet when elected pope, he will be ordained and then consecrated as a bishop. Usually, however, the pope is elected from the College of Cardinals, but that need not be the case.