David Norgrove said rising life expectancy meant millions of people would "undoubtedly" have to wait longer in future to draw a state pension. People will not save as much for retirement as in the past, with many people "frightened" to do so, he said.
Currently, the state pension age is 60 for women and 65 for men, but four years ago Lord Turner published a report calling for it to rise to 68 for everyone by 2044.
But Mr Norgrove said he thought it would end up higher. Mr Norgrove said:
"People are going to have to work longer, partly because we're not going, as a nation, to save as much for retirement as we did in the past."
He added: "The government's recent legislation is increasing the state retirement age progressively to 68. I think it will end up higher than that."
He said the ability of the current working generation to pay for the retirement of its predecessor would be "a real issue for the next 30 years", not least because of a lack of knowledge among the public about how to save. "The evidence is that people generally are frightened of saving for pensions," he said. "They think that pensions are very complicated. Actually, pensions in many ways are quite simple. Once you've made the initial decision you can let it run."
With life expectancy rising each year, many people argue that the government simply cannot afford to maintain state benefits at their current levels. Any potential shortfall has come sharply into focus following the massive increase in government debt amid the financial crisis, during which it has spent billions of pounds trying to boost the UK economy.