Thirty-year-olds should start plotting their retirement. Fifty-year-olds need to make younger friends and 60-year-olds must go back to school.

This is according to a book looking at how we can prevent one of humanity’s greatest achievements turning into a nightmare.

Andrew Scott, the co-author of The 100-Year Life, is publishing a treatise on 14 March: The Longevity Imperative. In it, he argues our lengthening lifespans are leading to a new era of humanity. “Get ready for fundamental change in what it means to be human,” he says.

Scott’s call has prompted a debate in the political and health spheres: James Bethell, a Conservative former health minister and peer, called it “the most important book of the year”.

He added: “It highlights that the current government has no vision or commitment to solving these issues. It’s sloppy, lazy and doesn’t take the health of our children seriously.

“The public gets what needs to change – it’s the political leadership that is the stumbling block, by which I mean the prime minister, clinicians, policymakers and the Treasury and the Office for Budget Responsibility, which doesn’t have the capability to track the impact of public health measures.”

Scott argues that without fundamental societal transformation, we are tumbling towards a dystopian near-future of spiralling health costs, a pensions crisis, mass dementia and overwhelmed care homes.

We are already part of the way there, he says. The pension age will rise to 67 in April 2026 amid a sustained rise in people out of work because of sickness, and only 9% of men and 16% of women born today can expect to reach state retirement age in good health.

There are 2.8 million people not looking for work because of health problems – a one-third increase on the 2.1 million before the Covid pandemic.

Approached differently, however, our longer lifespans could be the greatest gift humanity has ever been given, says Scott.

“This could be a takeoff moment in human history,” he said. “Ageing isn’t inevitable. It can be slowed down and even postponed. Ageing better is about increasing healthy life expectancy so it closes the gap with life expectancy.”

Retirement age should be linked to healthy life expectancy, not life expectancy, Scott says. But we need to prepare for our longer lives at ever younger ages. Instead of focusing resources on supporting old people, we need to help the young to become the healthiest-ever old people.

“If life expectancy continues to increase but healthy life expectancy and productivity increase too, there’s no need to raise retirement age,” he said.

Scott takes the government to task for reacting to longevity by simply raising the retirement age, lowering pensions and increasing taxes.

He claims the NHS is focusing on keeping people alive but not healthy – only 2.5% of total health expenditure in high-income countries is focused on prevention rather than intervention. He wants science to stop trying to eradicate single diseases and focus instead on slowing how we age.

Scott also says people are not planning far enough in advance to prevent later decades being plagued by ill-health, loneliness and poverty.

Dr Penny Dash, responsible for improving the health and healthcare of 2.5 million people in her role as chair of the North-west London integrated care system, said the NHS had spent the past 20 years attempting to shift resources out of hospitals and into primary care, community care and social care.

“Change, however, isn’t always popular and traditional perspectives of healthcare meaning hospitals remain,” said Dash, who has advised local, regional and national health systems globally.

“But with at least a third of hospital beds occupied by people who do not need to be there, and who risk losing muscle mass and independence in the process – and large numbers of people with undiagnosed and/or under-treated long term conditions, such as high blood pressure or diabetes – we clearly need to make more substantive changes over the next few years if we are to deliver improvements in health and quality of life.”

How to live a multi-staged life

1. Mix it up

Create multi-staged careers to fit with the multi-staged lives that come with longer lives. We have more years to be used – in our 20s, when we are discovering who we are, in our 30s, when we have small families, and in our 40s, when you want to retrain because you’ve still got 30 years of work left.

2. Be prepared

A multi-stage life will have a lot of ups and downs. We need to think about our finances, networks – professional and personal – and our identity. We need to build a wide range of options for different transitions at different times.

3. Back to school

We need to develop a lifelong focus on health and education. Keep in step with the future and continually scan for what you need next.

4. Diversify for the future

Think what your current role is teaching you that could be useful for later transitions. Are you working in a declining sector? Is your current job age-friendly? Do you have portable skills – can you imagine persuading a prospective employer of that?

5. Go beyond a peak

With a multi-stage life, a continued progression towards a higher salary is not the only goal. Think about what you will need at different ages.