Pictures: These are some of the world's oldest-elected leaders

Eighty-year-old Joe Biden, who announced on Tuesday plans to run again for US president, is among a handful of world leaders who continue to serve into their old age.

The world's oldest elected leader is Cameroon's president Paul Biya, 90, who has ruled for more than four decades. Ronald Reagan was still in the White House when Biya took the helm of the west African country in 1982. He won a seventh consecutive term in October 18.

Zimbabwean President Emmerson Mnangagwa: The 80-year-old has ruled the country since 2017.

Namibian President Hage Geingob, 81: a political veteran in power since 2014, he secured a second five-year term in 2019.

Ivory Coast President Alassane Ouattara, 81: Ouattara has been in power since 2011.

Irish politician-poet Michael Higgins, 82, has served as president of Ireland since November 2011. Popular for his everyman approach (he queues for cash himself at the ATM) and devotion to the arts, he was comfortably re-elected in 2018.

Italy's president Sergio Mattarella, 81, has been a unifying figure through five different governments and the Covid pandemic. The former constitutional court judge only wanted to be president once but finally agreed to stay on for a second term in 2022 after parliament, which elects the head of state, failed to agree on his successor.

Malta's 81-year-old George Vella is a former foreign minister, doctor and anti-abortion campaigner, who became president in 2019 on a promise to fight for "the respect for life from start to finish of every individual."