More than a quarter of British people will be aged 65 and over by 2066, jumping from less than a fifth today and increasing by a population around the size of London.
That is according to official life expectancy data published today, which shows that the number of over-65s is set to rise from 11.8 million to 20.4 million during that time.
However, the over-85 population is expected to rise fastest of all, doubling from 1.6 million to 3.2 million by mid-2041, and more than trebling to 5.1 million by 2066.
Aegon pensions director, Steven Cameron, said the findings highlight the ongoing challenges facing social care, and raise questions about when people should get access to the state pension.
"We need to make sure we protect those, who through health or work pressure, find it unfeasible to work to an ever-increasing age," he continued.
"There's an increasing need to allow those who can't work to advanced ages to opt to take their state pension from a younger age, suitably reduced to make it cost-neutral."
Today's data shows there will be approximately 393.6 people for every 1,000 in the population that are over the state pension age by 2066, up from 295.7 in 2017.
It also reveals that there are around 850,000 older people with dementia today, but that this could rise to one million by 2025, before doubling to two million by 2050.
In addition, it is predicted that half of baby girls will to live to 100 by 2066, up from 28.3% today, while the number of boys living to this age will jump from 22.6% to 44.2%.
Cameron said this would have important implications for the economy, with the data also showing that more than 10% of the over- 65s now work, compared with 5% in 1998.
"The key is to offer people the opportunity to remain economically active for as long as they want, and remain fit and healthy," he said.
"The UK is ahead of other EU countries, with individuals in the UK more likely to want to transition gradually from work to retirement rather than a 'sudden stop' at state pension age."
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