Here's an interesting fact about millennials that may not haveoccurred to you: This year, the oldest members of that generationare turning 37. By any definition, that puts them well intoadulthood.

1996 cutoff year for millennials

Pew Research Center,which has been studying millennials since 2007, announced last weekthat it would use 1996 as the last birth year for this cohort inits future work in order to keep the grouping analyticallymeaningful.

That means people born between 1981 and 1996— turning 22 to 37 thisyear — will be considered millennials.Those born in 1997 and later will be part of the next generation, amoniker for which is yet to be decided.

Related: Stages of financial life different formillennials

Pew's announcement, written by the center's president, MichaelDimock, noted that generational cutoff years are not an exactscience, but should be seen mainly as tools that enable researchersto examine differences in public attitudes toward key issues.

16 year span

No formula exists for how long a generational span shouldbe, Dimock said. Pew's span will be 16 years, he said, thesame as that of Gen X (those born between 1965 and 1980), but threeyears shorter than that of baby boomers (1946 to 1964), the onlygeneration officiallydesignated by the U.S. Census Bureau.

“Unlike the boomers, there are no comparably definitivethresholds by which later generational boundaries are defined,” hesaid. “But for analytical purposes, we believe 1996 is a meaningfulcutoff between millennials and post-millennials for a number ofreasons, including key political, economic and social factors thatdefine the millennial generation's formative years.”

Dimock summarizes these factors:

• Politics: 9/11 attacks; wars in Iraq andAfghanistan, contributing to political polarization; PresidentBarack Obama's election, thanks in part to the youth vote
• Economy: The 2008 recession has shapedmillennials' life choices, future earnings and entrance toadulthood
• Technology: Millennials have come of ageduring the internet explosion

According to Dimock, Pew will remain open to recalibrating itsanalytical line if a clear, singular delineation emerges as moredata are collected. “But more than likely the historical,technological, behavioral and attitudinal data will show more of acontinuum across generations than a threshold.”

'Accident of birth'

This means that differences within generations may be just asgreat as those across generations, with some thinking they havemore in common with bordering generations than the one in whichthey have been placed by accident of birth.

Last week, Pew issued a report that looks at several of its longest runningtrends in political and social attitudes and values.

On Tuesday, JohnQuiggin, a senior research fellow in economics at theUniversity of Queensland, argued in a New York Timesop-ed piece that Pew would have been better advised to abandon“what I call the 'generation game' — the insistence on dividingsociety into groups based on birth year and imputing differentcharacteristics to each group.”

Analyzing people in terms of generations, he wrote, “ultimatelydoes more harm than good by obscuring the individual factors thatactually shape our attitudes, politics and opportunities.”

Related: Move over millennials: Here comes GenZ

Michael S. Fischer is a regular contributor to ThinkAdvisor,focusing on tax and estate planning, philanthropy and other wealthmanagement issues. Contact him at [email protected].