Pope Benedict's resignation has placed the spotlight on octogenarians at the forefront of politics and business, who sometimes shoulder a workload that people 20 years their junior may shun. The 85-year-old pontiff announced on Monday that old age had sapped him of the strength required to lead the world's 1.1 billion Catholics. Benedict had a heart pacemaker installed some time ago but was not suffering from poor health, a Vatican spokesman said. It had not been generally known that the 85-year-old pope had been fitted with a pacemaker. His decision immediately raised questions about contemporaries who continue to hold on to the reins despite their advanced age. They include Britain's Queen Elizabeth, aged 86; King Bhumipol Adulyadej of Thailand, 85; Israeli President Shimon Peres, 89; and President Robert Mugabe of Zimbabwe, 88. In business, there is media tycoon Rupert Murdoch, 81; TV and film magnate Sumner Redstone, 89; and Hong Kong property supremo Li Ka-shing, 84. At 82, US actor and director Clint Eastwood is still going strong, while the French Armenian singer and diplomat Charles Aznavour still croons at 88. In rich countries, a large number of octogenarians are in good health, said Francoise Forette, director of the French national Gerontology Foundation. Figures show that only 17 per cent of 80-plussers are made dependent by disease, she said. Eyeing demographic trends, she said: "There are and there will be more and more people aged 80 and over who are able to shoulder the heaviest responsibilities." There are and there will be more and more people aged 80 and over who are able to shoulder the heaviest responsibilities But Forette and others also pointed to the growing health risks associated with ageing - and whether an individual actually wishes to carry on working a demanding job at an advanced stage of life. Last month Queen Beatrix of the Netherlands cited her 75th birthday as a reason to step down, saying "our country should be in the hands of a new generation". South Africa's Nelson Mandela retired as president aged 81 in 1999 and from public life four years later as his health declined. "You are not as energetic at 86 as you are at 40. When you reach that age, you are more fragile - fragile in your movements, fragile getting up," said Parisian gerontologist Olivier Henry. "Even walking is more difficult, as the muscles become weaker." According to the World Health Organisation, the number of people aged 60 and older has doubled since 1980 and is forecast to reach two billion by 2050 - a fifth of the global population. Almost 400 million of them will be aged 80 or above, the UN's health agency says on its website. "This population ageing can be seen as a success story for public health policies and for socioeconomic development, but it also challenges society to adapt, in order to maximise the health and functional capacity of older people as well as their social participation and security," it states. The health risks for the elderly are many: heart disease, stroke and chronic lung disease, visual and hearing loss, dementia and osteoarthritis … the list is long. They also sleep less and tire more easily - something that is particularly hard to handle when one's workload includes as much globetrotting as that of a pope.