Grey power: World's oldest leaders

With two septuagenarians -- 77-year-old Joe Biden and Donald Trump, 74 -- facing off for the US presidency, a look at the world's oldest leaders.

The world's oldest elected leader is Cameroon's 87-year-old President Paul Biya.

Although "The Sphinx" has been in power for nearly four decades, he is a mere stripling compared to Malaysia's 95-year-old Mahathir Mohamad, who only stepped down as prime minister in February.

With 68 years on the throne, Britain's Queen Elizabeth II holds the record for the longest period in office. Now 94, she is the head of state of 16 countries including Canada and Australia.

Cuba's Raul Castro -- the younger brother of the late leader of the country's revolution, Fidel Castro -- is 89.

Laos' communist President Bounnhang Vorachith is 83, although he is a relative new boy having only risen to power in 2016.

Guinea's Alpha Conde, 82, the country's first freely elected president, won a highly disputed third term last month.

Saudi Arabia's King Salman, 84, does not have such concerns but has delegated much of the responsibility for his oil-rich kingdom to his son, Prince Mohammed bin Salman.

The Middle East has a cluster of some of the world's most powerful octogenarians.

Iran's supreme leader Ayatollah Ali Khamenei is 81 while Lebanon's President Michel Aoun is 85 and Mahmud Abbas the head of the Palestinian National Authority is nearly 85.