Empty nesters are locking up America's family-size homes, according to a recent Redfin report.

Why it matters: "OK Boomer" might sting more when it comes from millennials eyeing the keys to your three-bedroom house.

State of play: The problem for many younger families is baby boomers don't have much motivation to sell, according to Redfin senior economist Sheharyar Bokhari.

• Boomers typically have low housing costs, and most of them "are only in their 60s, still young enough that they can take care of themselves and their home without help," Bokhari said in the report.

What they're saying: Chicago-area homeowner Neil Coleman says he doesn't plan to downsize anytime soon, partly because townhomes can add steep homeowners association dues.

• A smaller home probably wouldn't shrink their monthly expenses much, says Coleman, who tells Axios the house he's lived in for nearly two decades is paid off.

Reality check: Seniors are still downsizing, sometimes to luxury apartments.

• Of 1,020 boomers Opendoor surveyed nationwide who plan to sell their home, 85% said they intend to do so in the next three years.

The big picture: Homeowners nationally are holding on to their homes nearly twice as long as they did in 2005, Redfin research shows.

• Many of those staying put are aging in place. Most baby boomers who own houses are mortgage-free or have a low interest rate, according to the brokerage.

Between the lines: Homeownership has only gotten costlier. For many millennials around the country, the only way to buy a house is with family help.

What's next: Many young families are renting single-family houses.

• Those who want to purchase a spacious home should consider new construction, especially since some builders offer perks like mortgage-rate buydowns, Bokhari said.

Go deeper: America's homebuyers are getting older