Handing in your proverbial badge as a sexagenarian has been the goal for many workers around the world: turning 65 would open a golden portal to retirement. Yet increasingly, the idea of stepping away from the workforce in your 60s doesn't seem realistic – or even sensible – for many people, especially now. Some major financial figureheads agree.

In March, investment-management firm BlackRock released its annual letter to the company's investors. Its CEO Larry Fink sounded a warning for workers hoping to retire – comfortably and financially secure – in their 60s. As global life expectancy grows, social safety nets fray and cost of living spikes, Fink warned that retirement at age 65 won't be possible for many, even most, people.

"[Retirement] is a much harder proposition than it was 30 years ago," wrote Fink. "And it'll be a much harder proposition 30 years from now."

From 2000 to 2019, global life expectancy increased from 67 years to 73. By 2050, the UN expects one in six peopleworldwide will be aged 65 or older. And as the population ages, many countries will soon reach a point where more people are leaving the workforce than are entering it: in the UK, that point may be reached by 2029; in Brazil, by 2035; in India, by 2048; and in the US, by 2053.

"Life expectancy has been continuing to go up since the mid-1850s in the UK," says Rebecca Sear, professor of population and health at the London School of Hygiene and Tropical Medicine. "But the retirement age hasn't changed that much."

As both the health and economic landscape has changed dramatically, is retirement at 65 an entirely unrealistic goal in a modern world?