America’s slowly aging senior population is like a slow-moving freight train. Every day, more than 10,000 Baby Boomers pass the age of 65, and by 2050 seniors will make up 21% of the population (81.7 million). Despite this clear data from the U.S. Census Bureau, the supply of senior housing will soon fall short of demand, and in many cities, it already has.

Forbes recently released a list of the the U.S. cities with the most rapidly aging population. And while some cities aren’t particularly big draws for Millennials (Tucson, Phoenix, Las Vegas), the other cities on the list are some of the most popular destinations for young people and recent college grads.

Atlanta, Raleigh, Portland, Denver, and Austin were all named on the list of rapidly aging cities, and at a time when more people are renting than ever before, a housing crisis is slowly building in many cities.

The Urban Land Institute recently reported that one in two Millennials are renters, compared to just 35% of the overall population. In Denver, where real estate and rental prices are rising fast, Millennials and seniors often end up competing for the same coveted apartments for rent.

Which means trendsetting hipsters are squaring off against their elders for a dwindling supply of affordable housing. Both groups have their own unique economic challenges. Young people are struggling under an epic $1 trillion in combined college debt, while many U.S. seniors are on a fixed income or Social Security.

Aside from the most rapidly aging U.S. cities, Forbes also counted down the cities with the highest share of older citizens. Overwhelmingly, these cities are located in the country’s Rust Belt, where many young people leave for cities like Atlanta, Raleigh, Portland, Denver, and Austin.

Sadly, an incident in the New York City borough of Brooklyn might be a sign of things to come. Residents of the Prospect Park Residence in Park Slope, a long-term care facility for seniors, were evicted in March 2015 with only 90 days’ notice — so that the landlord could build new luxury housing units.

“It created such a panic. There are so few options, especially in Brooklyn,” said Myra Melamed, whose late father was given 90 days to leave the building. “Just to get on a waiting list takes a few months, especially for people with dementia.”