evidence: A significant proportion of people over 65 have some impairment of executive function, "I think as a general break point, 65 is reasonable," says Mark Fisher, who directs the Center for Neuropolitics at the University of California, Irvine. Other structural changes in the brain become solidified around this age as well – mental processing speed has been shown to decline from around the age of 60 in a study using US data. [...] The very loose threshold of 65 applies to the US, where the overall life expectancy at birth is 76. However, it may be different in countries with markedly different life expectancies and health systems (and there is also substantial racial and other inequality within the US that affects longevity). For example, the life expectancy for men in the US is 73. This is lower than in the top countries, but much higher than the life expectancy of 60 for men in Cameroon, whose president, 90-year-old Paul Biya, is said to be the world's oldest national leader. [...] However, the concept is highly controversial and politicised. Republican presidential candidate Nikki Haley has been leading calls for politicians over the age of 75 to undergo mental competency tests. But the approach has been criticised as ageist and difficult to implement. At the start of 2024, Haley went further by launching an series of politcal adverts that focused on Biden's and Trump's ages, including one that depitced the pair as the lead characters in the 1993 film "Grumpy Old Men".