NEW YORK • During the past decade, many US cities have been transformed by young professionals of the millennial generation, with downtowns turning into bustling neighbourhoods full of new apartments and pricey coffee bars.
But soon, those cities may start running out of millennials. Demographers, along with economists and real estate consultants, are starting to wonder what urban cores will look like now that the generation is cresting.
Millennials are generally considered to be those born between the early 1980s and late 1990s or early 2000s, and many are ageing from their 20s into the more traditionally suburban child-raising years. There are some signs that the inflow of young professionals into cities has reached its peak, and that the outflow of mid-30s couples to the suburbs has resumed after stalling during the global financial crisis.
Professor Dowell Myers, a professor of demography and urban planning at the University of Southern California, has published a paper that noted US cities reached "peak millennial" in 2015. Over the next few years, he predicts, the growth in demand for urban living is likely to stall.
Apartment rents have started to soften in some big cities because of a glut of new construction geared towards urban newcomers - who have not arrived. Rents in San Francisco, Washington, Denver, Miami and New York are also moderating or declining from a year ago, according to US real estate firm Zillow.
The debate really boils down to this: Are large numbers of millennials really so enamoured with city living that they will age and raise families inside the urban core?
Their choices will affect billions of dollars' worth of new apartments built expecting that the flood of young people into cities would continue unabated.
Many things affect the popularity of city living in the US, including lower crime rates and a preference for walkable neighbourhoods - but one of the biggest factors is how many fellow residents are also around 25.
Although apartment developers responded to the trend with a boom in new construction, in 2013 the number of people moving into and out of cities started to balance out for the first time since the recession, largely because people in their 30s and 40s have resumed their march to the suburbs, according to research by Professor Kenneth Johnson, a demographer at the University of New Hampshire.
The counter-argument, though, says "this time is different".
And millennials do seem to like cities more than their parents. Mr Joe Cortright, director of the City Observatory, an urban think-tank in Portland, Oregon, is predicting that this time cities will continue to swell - both with young people coming in and older people staying longer.