Yet many government programmes continue to use it as a standard. In the US, Medicare, the federal healthcare insurance program, is currently available only to adults aged 65 and older (there are exceptions for younger people with disabilities). Americans become eligible to receive their full Social Security benefits at age 67, roughly the same age that UK citizens can claim their universal State Pensions.

In the mid-20th Century, when many of these programmes were enacted, life expectancy was significantly shorter: in the UK, for instance, it was roughly 66 years for men and 71 years for women. “If you’re basic about it, [UK citizens would] only spend 8% or 10% of their life on a pension,” says Chris Parry, principal lecturer in finance…