A group of people who believe they belong to a clearly defined generation, but who don't. (Bonnie Jo Mount/The Washington Post)

If you were born in 1948, you are a Baby Boomer. If you were born in 1978, you've probably been told that you are in Generation X. Born in 1988? You have been told that you're a Millennial or, a decade ago, that you were in Generation Y. Just born? You cannot read; you don't fool me.

But now a little real-keeping. Only the person born in 1948 has not been lied to. Everyone else? You don't really belong to any clearly defined generation. At least, not yet.

We obsess over our generations the way we obsess over our horoscopes, recognizing that it's a dumb approximation of who we are but mining every description for the details that we think are correct. The advent of the clickbait Web has meant that we're awash with "You know you're a Millennial if" or "22 things only Gen Xers will remember" nonsense. And we mean "nonsense" in two ways: Those stories are usually fluff, and from a demographic perspective, the idea that Generation X is a set generation is nonsense.

The unofficial government arbiter of what is and isn't a generation is the Census Bureau. Its catalog of aggregated data on the lives of Americans recognizes only one official generation: The Baby Boomers. Howard Hogan, the bureau's chief demographer, explained why in an e-mail to the Post. "The Baby Boom is distinguished by a dramatic increase in birth rates following World War II and comprises one of the largest generations in U.S. history," Hogan wrote. "Unlike the baby boom generation, the birth years and characteristics for other generations are not as distinguishable and there are varying definitions used by the public." So the Census Bureau will put together numbers for Boomers, because that's a real, demographic generation. It doesn't release numbers on "Millennials" because you made that term up.

A quick survey of news reports on the different generations over time shows how generational indicators rise and fall. The chart below shows different proposed names from different time periods, spanning the length of each colored bar (or, when a start or end is nebulous, indicated in a lighter color). You think you're in Gen X, but 30 years ago, you'd have thought you were a Baby Buster. (Edit0r's note: I prefer Gen X.) You think that college kids are Millennials, but a decade ago some people might have called them "Nexters." (And little newborn baby reading this? The Times says you're Generation Z. I'll assume you probably do read the Times.)

[We dismantled the White House's attempt to clearly define generations last year. WWCBD*]

"From a demographic perspective, it's not clear to me why those boundaries are drawn as they are," said Mark Mather, a demographer with the Population Reference Bureau. "It seems fairly arbitrary, for example, to put Gen X from 1964 to 1980, which is only a 16-year period. It doesn't really even span what most people would consider a generation." Unless you think that most children are born to high school sophomores.

"A lot of demographers will tell you that we like to work with cohorts, as opposed to generations," he explained. "We're always looking for ... demographic patterns: Marriage, fertility, family formation, those types of things." The Baby Boomers were themselves a cohort: a group that shared a certain set of demographic characteristics. Generation X doesn't.

In its work, the Pew Research Center uses generational boundaries like "Millennial" (which it defines as those born between 1981 and 2000, a somewhat early end point compared to others). "They are somewhat arbitrary," said Kim Parker, director of social trends research at Pew, of the generational descriptors. But generations as a concept can be "a worthwhile tool for storytelling, taking a lot of data and trying to put it into an interesting prism that speaks to people."

She acknowledges that this can yield a negative result. "A lot of times, people are frustrated. They think, 'I'm not a Millennial! I don't feel those same things in the way that you're generalizing.' That's one of the shortcomings." Parker has advice for those who are on the bubble between two identifications. "Pick the younger generation, of course!" she said. She also pointed out that there is "real bleeding across lines" in terms of what makes a "generation" unique. So if you feel like a Millennial, say you're a Millennial, who cares. (Here, take Pew's "How Millennial are you?" quiz.) Generations are like "Whose Line is it Anyway?": The boundaries are made up and the labels don't matter.

Except. Every so often, there's a generation, like the Boomers, that hangs together as a distinct demographic cohort. And maybe, just maybe, the Millennials will eventually be determined to have met that standard.

"Right now, we're in a kind of a unique period where young adults are undergoing some rapid demographic changes," PRB's Mather said. "They're getting married much later; fertility rates are dropping. If some of those changes become long-term, I can see that today's young adults might fall into some new cohort that we can define based on their unique characteristics."

Meaning that Millennials might join Boomers in being a defined group that even the cautious Census Bureau sees fit to recognize. And wouldn't that just be like the Millennials? That group, born between January 1, 1981 and December 31, 2003, is always so desperate for attention.

* What would the Census Bureau do? We also would have accepted: What would Charles Barkley do?