The world is graying. Globally, 55-year-olds will outnumber 5-year-olds by 2020, and by 2050, the number of people aged 50 and older will rise to 3.2 billion, a twofold increase since 2015. In the United States, those 50 and older accounted for $7.6 trillion of economic activity in 2015, almost half the country’s gross domestic product. Worldwide, spending among older consumers could reach $15 trillion next year .

Marketers have it wrong. The most important consumer group isn’t the 18-to-24 set, as conventional business wisdom has it. It’s older adults.

There are several reasons why: People are living longer, the global birth rate is dropping, and baby boomers are aging. These trends underscore more than a demographic blip; they suggest a long-term pattern that will reshape the economy and society at large. “The aging of populations represents the most profound change that is guaranteed to come to high-income countries everywhere, and most low- and middle-income ones as well,” writes Joseph F. Coughlin, founder and director of MIT’s AgeLab and the author of The Longevity Economy. “There may be other big shifts headed our way–related to climate change, say, or global geopolitics, or technological advancement–but their particulars are still up in the air. We can only speculate about how London will cope with sea-level rise, or Tokyo with self-driving cars. But we know exactly how global aging will unfold.”

The imperative for businesses to better serve aging populations is clear. You don’t need to look hard to see that the world is designed abysmally for older adults, from microscopic screens to packaging that can’t be opened easily to broken elevators and inaudible announcements on public transportation.

Some companies simply overlook the senior market. Others try catering to it and misfire wildly. Think of all the daytime television ads for beige pill sorters and personal alarms that portray older adults as helpless and needy. In a 2014 survey of people ages 70 and older cited in The Longevity Economy, less than half the respondents felt that commercials represented their age group in a respectful way.

This isn’t necessarily a failing of individual companies. Rather, it’s a societal failure to understand the value of older people–to see aging as a welcome progression of life, rather than an inconvenience.

In our series The New Business of Growing Old, we hope to offer a corrective. We tap Don Norman, inventor of modern usability studies and a proud octogenarian, to demystify some of the wants and needs of older consumers. We examine burgeoning economies, such as senior co-housing and end-of-life wellness. We talk to sex expert Joan Price on fun, healthy sexuality in older age. We ask Chip Conley, former head of global hospitality and strategy at Airbnb, for tips on embracing the wisdom of elders. The through line? What benefits older people typically benefits other demographics, too.