(Pope Benedict XVI leaves at the end of the Sunday Angelus prayer in Saint Peter's Square at the Vatican April 15, 2012. REUTERS/Tony Gentile )

Pope Benedict marks two milestones this week and while his health appears stable, signs of frailty have again prompted speculation over whether he will be the first pontiff in seven centuries to resign.

Benedict, one of the oldest popes in history, turns 85 on Monday, and on Thursday he marks the seventh anniversary of his election as successor to the immensely popular John Paul II.

Speaking to pilgrims and tourists in St Peter’s Square on Sunday, he noted Thursday’s anniversary and asked for prayers “so that the Lord may give me the strength to carry out the mission he has entrusted to me”.

Benedict is already older than John Paul was when he died in 2005 and is now the oldest reigning pope since Leo XIII, who died aged 93 in 1903 after reigning for 25 years.