Today's children could live to 120 and work until they're 100, it's been claimed. But which occupations might they take on?

Imagine you went to a football stadium and the steward who showed you to your seat was 93 years old.

Today, most people might find such a sight surprising. But Rohit Talwar thinks that, within a century, this kind of work could be done just as easily by a nonagenarian as a twentysomething.

"If you go to a football match the stewards are usually young guys who get abuse from the fans, who don't worry about upsetting them," he says. "But if someone's in their 90s, they might be more wary of getting physical with them."

He or she might also go on to be a counsellor, a classroom assistant, a building instructor or a chef - after a later career change.

Talwar, a futurologist, has made headlines by telling the Headmasters' and Headmistresses' Conference that many of today's 10 or 11-year-olds will live to at least 120 and a sizeable proportion will keep working until they reach 100. But how might this work?

Scientific advances, such as replacement limbs made by 3D printers, powered exoskeletons and memory-preserving drugs will allow today's children easily to outlive their parents and keep active, Talwar says.

"They might not want to continue at quite the same pace after decades in the workplace," he says. "But they will be able to make work fit in with their lifestyles."

There will still be lots of roles requiring human beings, in which experience comes at a premium, Talwar argues.

"But more and more of the physical tasks of work will be done by robots. They can carry and fetch and work 24 hours a day," he says.

The calm and wisdom of age could be useful assets in the classroom, Talwar says. A large number of people aged 80 to 100 working here would be a major change, as, according to the latest figures for England, just over 2% of state school teachers are 60 or older. There aren't equivalent statistics for classroom assistants.

With such long working lives, Talwar predicts that workers will adopt a "portfolio" approach to employment, meaning they could have as many as 10 different, shorter careers, including 40 different jobs. People could do more than one job in a day, he says - perhaps driving an Uber cab in the morning and delivering Amazon parcels in the afternoon.

There will be a more "sharing economy", where the line is blurred between employment and other money-making activities, such as renting out spare bedrooms and driveways using services such as Airbnb, he adds.

Demographics are edging towards Talwar's predictions. The UK population is ageing, as is that of its main competitor economies. The number of people over the age of 90 was more than half a million last year, according to the Office for National Statistics (ONS).

Included in this category were 14,450 centenarians. And the number of people living to 105 or older was 780 - double the figure of a decade earlier.

But even should these trends continue, will a standard retirement age of 100 really be possible by the year 2100? Will people be in good enough mental and physical condition to work for up to 80 years?

"We are entering a new era of longevity in terms of life expectancy. But it seems we're also entering a transformational time in terms of the way work happens," says Sarah Harper, director of the Oxford Institute of Population Ageing.

"Just compare now to what happened 100 years ago or so. Then, many women died in their 40s because of having to give birth many times. Lots of people died young."

Harper predicts that most jobs as we know them will no longer exist when today's children reach 100. Robots will work alongside humans, making physically demanding tasks obsolete, while working patterns will be less regimented, instead fitting around lifestyles and family time, she adds.

"There's not a lot in the modern workplace that many 70-year-olds couldn't cope with today," says Harper. "Eighty-year-olds may be more variable in their capacity, but that will change.

"By then, many 100-year-olds could be able to do the same as 65-year-olds, or even 50-year-olds, today. And, if you look at it like that, what is there that a 50-year-old can't do in most workplaces that 30 or 40-year-olds can?"

But not everyone's as optimistic.

"None of the evidence we have shows people being able to go on working until they're 100 years old," says Neil Duncan-Jordan, national officer for the National Pensioners Convention.

"We can keep people alive until then, but that's a completely different argument to saying they should be able to drive a bus. I think the whole idea's a bit sci-fi. It's nonsense." People should be able to retire in their 60s, expecting "20 years of decent living", he says.

The number of over-65s in some form of paid work is 1.14 million, according to the latest ONS figures, equating to 10.2% of that age group.

The phenomenon is touched on the recently released comedy film The Intern, starring Robert De Niro as a 70-year-old widower who grows bored of retirement and lands work experience at a fashion website. Initially out of place among the otherwise youthful workforce, he becomes a friend and mentor to this colleagues.

That role is office-based, but a "surprising" portion of working over-65s do physical jobs such as bricklaying, says Chris Brooks, head of employment and skills policy at the charity Age UK, while many others do "demanding" work in the retail sector, which includes tasks like shelf-stacking and moving stock.

He finds it "difficult to name specific" jobs that a 100-year-old might be able to do in the future, should predictions of increased longevity come true, but adds: "If people want to work and they are able, there should be no barrier to them doing that. For some people it's important to their self-esteem and provides a social network."

People will have to spend more time in education well into adulthood, Talwar says, as they re-skill to deal with an altering jobs market.

"After all, who would ever have thought until recently that you'd need social workers specially trained to deal with the traumas caused by social media?" says Talwar. "Things change."

Article from BBC