Two separate reports for the government have raised the possibility that millions of people may have to work longer to qualify for a state pension.
An analysis for the Department for Work and Pensions (DWP) has suggested that workers under the age of 30 may not get a pension until the age of 70.
A second report, by John Cridland, proposes that those under the age of 45 may have to work a year longer, to 68.
The government is due to make a decision on both reports by May.
Ministers are under pressure to address the expected rise in the cost of pensions, which stems from longer life expectancy and the increasing ratio of pensioners to workers.
But at least six million people face the prospect of having to work longer.
"This report is going to be particularly unwelcome for anyone in their early 40s, as they're now likely to see their state pension age pushed back another year," said Tom McPhail, head of retirement at Hargreaves Lansdown.
"For those in their 30s and younger, it reinforces the expectation of a state pension from age 70, which means an extra two years of work."
In an extreme scenario, experts from the Government Actuary's Department (GAD) said the state pension age could be raised as high as 70 as soon as 2054.
Under existing plans, the state pension age is due to rise to 68 for those born after 1978.
The "extreme" scenario involves an assumption that people spend 32% of their adult life in retirement. The conventional assumption until now has been that people will spend 33.3% of their lives in retirement.
In the worst-case situation, the GAD calculations also suggest that the change in the retirement age from 67 to 68 could be pulled forward by as much as 16 years.
So while that increase is not due to happen until 2044, it could be brought in as soon as 2028, affecting those now in their late 50s.
Former pensions minister Steve Webb was highly critical of the GAD's scenario.
"This is not what parliament voted for and is clearly driven by the Treasury. It is one thing asking people to work longer to make pensions affordable, but it is another to hike up pension ages because the Treasury sees it as an easy way to raise money," he said.
However, the other report, by the former CBI chief John Cridland, foresees more modest changes.
He recommends bringing the change from 67 to 68 forward by seven years, from 2046 to 2039. That would mean anyone currently under the age of 45 having to work an extra year.
The changes are due to be phased in gradually, over a two-year period in each case.
In addition Mr Cridland said there should be no up-rating from 68 to 69 before 2047 at the earliest, and that the pension age should never rise by more than one year in each ten-year period.
He also suggests that the so-called triple lock be ended in the next parliament.
Up to now the triple lock has guaranteed that the state pension rises each year by inflation, earnings or 2.5%, whichever is the highest.
However, by linking the rise in pension payouts to earnings alone, the bill for pensions would fall from 6.7% of GDP to 5.9% of GDP by 2066.
Mr Cridland also recommends:
- A new system of carer's leave, allowing older people with caring responsibilities to have time off work
- A mid-life "MOT" to help people take decisions about work, health and retirement
- Some vulnerable people in their 60s should have access to a means-tested benefit, along the lines of pension credit
- There should be no "early access" to the state pension, despite this being raised as a possibility in the interim report
- People could defer drawing their pension, taking higher benefits later