Last year, Greta Thunberg shot to fame as the poster girl for climate-change activism at the age of just 15. By 16 she had a Nobel Peace Prize nomination. Inspired, children around the world have been skipping classes to demand action on climate change.

Young people, though, can do little more than protest. After all, it’s not the young who make the big decisions, but the middle-aged.

People between 45 and 65 rule our societies: the median age of an incoming US senator is 51, the average age of a British member of Parliament is 50, and the average age of a CEO in Fortune 500 and S&P 500 companies is 53. There are exceptions, of course—Facebook CEO Mark Zuckerberg is just 35, while Donald Trump is 73. On the whole, however, it is the middle-aged who hold the reins. Younger generations lack the experience and influence needed for the top jobs, while older ones succumb to ill health or simply social pressure to step down. Today we might approach society’s elders for advice or consult them for their wisdom, but it’s the middle-aged who choose whether to act on that advice, who decide how to implement that wisdom.

If medicine can keep us healthy and sharp for longer, though, tomorrow’s 80-year-olds could do the work of today’s 50-year-olds. They could be just as fit, and they’d have extra wisdom and experience to boot. It’s very possible that by the turn of the next century, society’s movers and shakers could be in their 80s, not their 50s.

What happens then? Contemporary views of generational roles will make less sense in a world that relies on the old to run politics, culture, and the economy.

There are risks, of course. If the most important decisions are made by the old, then the interests of the old might edge out those of other age groups. This could exacerbate the sort of intergenerational inequality we already see today. Compared with earlier generations, millennials have less money and more debt. Having each generation hang onto power for longer could make successive generations not only even poorer, but increasingly powerless. We’ll need to change the way political decisions are made to ensure that the interests of all ages are fairly represented. And to make that happen, we’ll need changes at the grassroots level, such as overcoming the taboos that prevent free, frank, and constructive discussion of death, inheritance, and what the old owe the young and vice versa.

The middle-aged face demotion when their elders show no signs of slowing down—but what about younger people? What will it be like to be in your 20s and 30s in a society where people live until 100 or more and continue to work into their 80s? Today, young people don’t earn as much as the middle-aged, and they have lower status and less influence. They do have youth on their side—a great asset in Western societies where the entertainment and fashion industries are dominated by them, and where they are an important consumer group. But the value of youth itself is likely to be eroded in the future. After all, if tackling ageism will be a necessary part of getting the most out of an aging society, then progress will mean attacking a beauty industry peddling “anti-aging” products, a movie industry focused on telling the stories of young people, and a music industry where performers are past their peak by their mid-30s. In a world that no longer celebrates and commodifies youth, young people risk being resented as a drain on the economy, as people who have not yet accumulated sufficient experience to make a useful contribution to society—and if future generations of the young are poorer, they will be literally less valuable as well.

It might be difficult to conceive of this happening very quickly—but it is difficult to conceive of it not happening, too.

Even so, there is hope. Defeating ageism, like defeating any kind of bigotry, will involve undermining the stereotypes associated with it. Efforts to address ageism often focus on dismantling ideas that old people are lonely, depressed, demented, and irrelevant. But we needn’t (and shouldn’t) stop there. We should also tackle stereotypes that paint the young as irresponsible, naïve, and deserving of only the most menial jobs and lowest pay, or that present frivolous millennials as too busy munching on avocados to save for a house. Ending ageism against the old might take the shine off youth, but it will free the young of some unhelpful prejudices too.

Maybe what we can expect from people of different ages will become even more context-dependent.

Olympic swimmers peak at only 21. By contrast, the most successful scientists retain their influence until their death—as the German physicist Max Planck observed, science advances one funeral at a time. How much our mental and physical qualities enable us to excel or hold us back depends on what we’re trying to do and how much support we have. But ageism is so pervasive that we simply don’t know what tomorrow’s 80-year-olds will be like. We haven’t yet encountered a society with large numbers of older people able to flourish free from this oppressive prejudice.

An aging world could easily be a dystopia. Increasing life expectancy without improving healthy life span would lead to a sicker population and weigh down an increasingly burdened workforce. Delaying people’s retirement from influential, decision-making roles could lead to worsening social inequality, and the risk remains that some people—young and old—could fall through the cracks at times when they are less able to contribute.

How do we change that? If we focus on how individuals of any age can contribute, and recognize that people are able to contribute in different ways at different times, and ensure that there is support—such as finance, health care, training, and education—then we might be able to ensure that an aging society can also be a thriving one.

Rebecca Roache is a senior lecturer in philosophy at Royal Holloway, University of London.