Society will have to embark on some radical rethinking of everything from pensions to the work-life balance if it is to cope with increasing numbers of people living to be 100 and older, demographic experts have warned.

According to figures released this week by the Department for Work and Pensions, more than a quarter of children aged 16 and under can expect to see their 100th birthdays.

The statistics revealed that as many as 11 million people alive now will become centenarians: 3.3 million are aged 16 and under; 5.4 million of them are between 17 and 50; 1.4 million are 51-65, and more than 900,000 are already over 65.

The pensions minister, Steve Webb, said the state pension system had to be made "fair and sustainable for future generations" if people were likely to be spending more than a third of their lives in retirement. But others have suggested that a far more radical approach is required.

David Sinclair, head of policy and research at the International Longevity Centre, said that while the increase in life expectancy was "a huge societal success", it would come at a price.

"If the projections are true, then the impact on service provision is huge and as a society we are heading towards huge fiscal service pressures," he said.

"The pressures on local authorities and central government will have a very, very significant impact - as will the knock-on impact on other ages and other generations. If the older population demands more and more resources, then it has to come from their own wealth and assets - or from someone else."

That, said Sinclair, could form the crux of the problem. While the increased number of active and familiar centenarians might help change and improve our attitudes to older people, their ubiquity could give rise to resentment.

"The pessimistic side is that there is a very real risk that it could generate even more intergenerational tensions if you end up with a clash for resources between young and old - and that is what we really need to avoid."

Prof Jane Falkingham, head of the school of social sciences at Southampton University and director of the ESRC Centre for Population Change, said one of the challenges would be deciding when to work and when to have children.

"Although medical advances are pushing up the age at which women can bear children, the most fertile period is and is likely to remain the 20s and 30s," she said.

"One question is whether it makes sense to juggle work and family life, or whether we in future will invest in parenthood and then invest in work - and work into our 70s."

Such an approach, she said, would involve rethinking the way the welfare state works. "If people are going to restructure their lives and have their children first and then have work, they're going to have to have something to live on when they're having the children before they pay it all back through the world of work," she said. "So it's thinking about how the welfare state can operate across the life course, as well as how individuals restructure their lives."

Danny Dorling, professor of human geography at the University of Sheffield, said that while the ONS projections ought to be celebrated, they should not be taken for granted.

"It's good news that it's possible," he said. "But Britain currently has the lowest life expectancy of almost any western European country and we need to ask why.

"Japan has the largest number of old people in the world; Japan also has lowest income and probably the lowest wealth inequalities in the rich world."

Prof Sir Michael Marmot, of University College London, said it was high time for some "radical rethinking about what the nature of the life course looks like in a changed society".

Sir Michael - who led a government-ordered review into Britain's widening health inequalities last year - added that the projections would illustrate how variable outcomes could be for different people.

"We'll have some people working all their lives and not having nearly as much time to enjoy their pensions, and other people working all their lives and having decades to enjoy their pensions because their life expectancy is much longer.

"Unless we're going to take the kind of steps that my health and equality review called for - unless we're going to take the steps to reduce that - these new projections will mean much longer, healthier lives for some but not for others. It won't be uniform by any means."

Personal view: Diana Athill

An impressive person living in this retirement home is 105. She has all her marbles, walks far, far more briskly than the rest of us and has a positive and cheerful disposition. If anyone is a good advertisement for being a centenarian, she is.

Yet she says – not in a whingeing way, but calmly, as a matter of fact – that she has had enough. She would like to die. And I, while still six years short of 100, can see what she means.

However well you carry your old age, and however many surprising compensations you discover in it, it does get worse and worse. It is a limited condition. Your body is no longer a source of pleasure and although you can still do much, there are a great many things you can no longer do. It isn't, I'm sure, meant to last very long. After all, everything that has a beginning has an end. That's life.

So I think it's bad news that so many more people are going to reach 100 – I certainly don't want to be one of them. And one thing's for sure: we'll have to keep a very close eye on our lords and masters or they'll start contriving ways of polishing us off. We may not want to last very long but we don't want to be killed.

• This article was amended on 20 April 2011. The original referred to figures released this week by the Office for National Statistics. This has been corrected.