You might live to be 100. Are you ready?

At the age of 111, a British accountant named John Tinniswood has just been declared the oldest man alive. Asked for the secrets to his remarkable longevity, he mentioned his fondness for a plate of fish and chips every Friday. Mostly, he thought it was down to “pure luck”.

When Tinniswood was born in Liverpool in 1912, the idea of living to 111 would have struck his parents as fanciful, if not absurd. The average life expectancy of a British male then was 52 years.

By 1950, there were an estimated 14,000 people aged 100 or more worldwide. Today, there are more than 500,000, and their number is rising rapidly. Medical advances, increases in the standard of living and improvements in public health have transformed the human condition. The American Academy of Actuaries estimates that one in six Americans born today will live to be 100. A huge demographic change is unfolding, and many more of us can expect to share the “luck” of John Tinniswood.

Does the prospect of living that long excite you, or is it a source of dread? Do you look forward to decades of extra time or does living to 100 sound more like a threat? Plainly, there are reasons why we worry about living for so long. What’s the point of living beyond 80 if your savings have run out, the care homes are full, and you end up feeling lonely, bored and irrelevant?

For most of human history, these concerns were irrelevant. Only a minority could expect to become old. Now, with global life expectancy exceeding 70 years, it is a majority. The consequence is we can no longer afford to rely on luck to age well. Just as we debate adapting and adjusting to AI and the climate crisis, we need similar conversations regarding our newly extended length of life. Having got the majority to live to be old, we now have to focus on changing how we age to make life not just longer but healthier, productive and engaged for longer.

Longevity is about more than physical health, but it is this issue people fear the most. Today, there is too large a gap between average lifespan and healthspan. The number of years we are likely to live has increased more than the number of years we are likely to remain healthy. Reducing this gap is critical for seizing the advantages of longer lives.

The good news is that there is much you can do. Around 80% of how we age is driven by our behaviours and environment. It may sound tiresomely familiar, but there’s no substitute for eating and sleeping well, exercising more, and following your doctor’s advice. While that advice is being given a scientific upgrade, what has really changed is your incentive to follow it now you can expect to become old.

Luckily, though we don’t have to rely solely on self-discipline. Ageing well is becoming an industry, and we can expect support from technological and scientific progress and shifts in government policy. While the extreme longevity-inspired lifestyles of billionaires grab the headlines, you are more likely to be impacted by broad-based shifts in our health system.

These systems currently focus on intervening when a disease becomes so noticeable that it adversely affects your health. But when it comes to ageing-related illnesses, such as cardiovascular disease, cancer, diabetes or dementia, that is a recipe for keeping us alive for longer not healthier for longer.

Instead, the focus needs to be on exploiting the potential of modern prevention techniques, such as AI and big data. Whether it’s tracking your genetics to identify the diseases you are most at risk from; monitoring changes in your body’s biomarkers for early signs of disease; or accelerating drug innovation and repurposing, future innovations await.

Another stride forward will arise if we make further progress in understanding the biology of ageing – the processes that slowly diminish the physical components of our bodies. The prize is huge because slowing these down would substantially reduce the gap between healthspan and lifespan.

The mere notion of treatments that could delay ageing-related diseases is revealing of how humanity is entering a radical new era. We tend to think of ageing as “natural” and immutable, but that reflects our relatively recent progress in reducing the threat from diseases such as smallpox, cholera, tuberculosis and plague. For most of history, these diseases were considered “natural” and were the main reason so few lived into old age. That explains why, in the 17th century, Montaigne considered dying of old age a “rare death” and “less natural than the others”. Now that the main cause of death and illness is ageing-related diseases, scientific attention is turning to tackle this next frontier. How we age is malleable and exploiting that is key in a world of longer lives.

The result is increasing resources invested in what has become known as geroscience. Throughout history, there have always been those who claim to have discovered the secret of youth, but slowly the topic is being drawn into the mainstream scientific community. Progress is also being made in the lab such that manipulating the age of cells and extending the lives of an increasing range of animals is now routine.

None of this implies you’ll be popping magic anti-ageing pills anytime soon and it certainly doesn’t mean you can start dreaming of immortality. What it does mean, though, is that the younger you are, the more likely it is that you will benefit from treatments that help you age better. Exactly how far that takes us will depend upon the relative strength of human ingenuity and human biology, but it opens up a future which changes in fundamental ways what a human life looks like.

But if we can be healthier for longer there is another problem we have to tackle – how to pay for those extra years? If most of us live until 100, state pensions in their current form will collapse. Absent an AI-induced surge in productivity, living longer requires working longer if we are to maintain our standard of living. That is why governments worldwide are increasing retirement age. Once more we are back to the unpalatable consequences of living for longer.

But seizing the advantages of a longer life needs more profound adaptation than simply raising the retirement age. We need changes that help us work for longer, not just force us to work for longer.

We need to create a new, more flexible structure of work and leisure that extends far beyond raising the retirement age. Career shifts and transitions will need to become more frequent as we change jobs and occupations to prolong our careers, take time out to reskill or improve our health, care for family, and shift between full-time, part-time, or no-time work.

This restructuring of the life course reveals that the true benefit of longer lives is more time. We tend to think of longer lives as bringing time at the end of life, but the healthier we make those additional years, the more time we have over our whole lives. The 20th century saw growing life expectancy leading to more years of leisure after retirement. The longer careers of the 21st century will be about taking more of that leisure this side of retirement.

This leads us to perhaps the hardest change of all – seeing a longer life as an opportunity and overcoming deeply engrained ageist assumptions. Currently, we underestimate the capacity of older people and the promise of our own later years.

David Bowie, a man who knew a thing or two about transitions, described ageing as “an extraordinary process whereby you become the person you always should have been”. If we can make life not just longer, but healthier, productive and engaged for longer, what’s not to like?

For most of human history, only a minority of the young and middle-aged became old. The result is that we underinvest in our later years and fail to provide the support that a long healthy, productive and engaged life requires. Given how many of us alive can expect to become 80, have a shot at 90, and might even make it to 100, that is a problem which demands change.

There is much to be done. The malleability of ageing shows up dramatically in growing health inequality, a problem requiring urgent attention. Changing how we age requires major shifts in social norms and institutions. But that is the thing about long lives: they witness much change. When John Tinniswood was born, the concept of a teenager didn’t exist, and the United States hadn’t introduced a state pension. The years ahead will see equally substantive shifts in how we live as we respond to longevity. John Tinniswood didn’t expect to live so long and benefited from “pure luck”. The centenarians of tomorrow can have no excuse and cannot afford to rely on luck. We need to create a longevity society.

• Andrew J Scott is Professor of Economics at London Business School and author of The Longevity Imperative : Building a Better Society for Healthier, Longer Lives, Basic Books, 2024.