By 1909, the reformer Jane Addams worried that democracy “no longer stirs the blood of the American youth.” She argued that “never before have the pleasures of the young and mature become so definitely separated,” stifling the sense of a shared interest in public life.

Panicked campaigners felt this as well. Desperately trying to hold on to young supporters, the major parties created youth-only clubs, designed to recruit “beardless and boyish workers.” But without age mixing, these organizations fizzled, and turnout by first-time voters fell by more than 50 percent in the early 20th century, according to the historian Paul Kleppner.

Conventional histories often break the 20th century into a succession of discrete generations, jumping from Lost to Greatest to Silent to Boomers to Gen X to Millennials. With each generation, scholars invented new terms to discuss young people, many of which became media clichés. In the early 1900s, psychologists replaced the vague word “youths” with “adolescents,” meant to indicate a vulnerable stage during which young people needed to mature in isolation. In the years after WWII, “teenager” emerged, based on the idea that youth was not merely a phase, but an entirely separate culture, a world to be marketed to.

Americans used the word “generation” more and more across the century. If “adolescent” and “teenager” are temporary stages, the generations became permanent identities.

The growing separation of American age groups made it difficult for young people to participate in adult politics. The two periods when Americans seemed the most fixated on generational difference, from 1900 to 1929 and 1964 to 1980, both coincided with huge drops in voter turnout. And bursts of political excitement, like during the New Deal era, were usually followed by crashes in the political engagement. The problem was that, no matter how excited a cohort might become, they just couldn’t pass down their passion to the estranged next generation.

The Baby Boomers had particular difficulty borrowing from their elders or educating their juniors. As talk of the “generation gap” peaked in 1972, voter turnout among 18-to-29-year-olds began a decades-long slide relative to turnout by those over 30 in presidential elections. Generation X continued this slump in the 1990s, although Millennials have somewhat improved youth turnout since 2004.

Millions of well-intentioned activists are working to get those Millennials voting this November. And they’re doing a good job. But America has reached peak-Millennial: This is the last presidential election in which the youngest voters will have been born before 2000. If campaigners think about politics purely in generational terms, they’ll have to start over in four years.

Generations do play an important role in American politics, giving diverse groups something to unite around. But that strength is also a weakness: uniting a generation often means isolating it, bottling up its knowledge and excitement. In politics, and in the rest of life, age mixing has a power that is often neglected in this segmented, modern world—a power that once made schoolyards brawls and dinner-table debates the centerpieces of American democracy.

This election will be over in a few months, but each new voter will have an impact for decades to come. The 18-year-olds casting their first ballots may have a say in 15 or 18 future presidential elections. Some will shape the country into the 22nd century.

So forget generations. Stop chattering about Millennials. Blurring those age-based divisions will only help make American democracy more sustainable.