IN 2019, Ward Berlin and his wife, Karla Grazier, moved into a newly built house in a new Colorado gated community called Vermilion at Garden of the Gods. But they didn’t have to spend much time getting to know their neighbors: Many of the eight properties on their street were owned by friends they had known for years.

Brenda Smith and Judy Mackey, the developers of the 39-unit Colorado Springs community, planned to move in with their families and had offered the other lots to friends rather than putting them on the open market.

“There’s a big difference between a community and a neighborhood,” said Mr. Berlin, a 56-year-old private investor. Choosing neighbors who are also longtime friends, he said, lets him “spend more time with the people that I really care about.”

Members of the wealthy baby boom generation are meticulously planning their golden years, from first-floor master suites to who their neighbors will be. Groups of friends—many of them empty-nesters—are increasingly buying properties in the same housing developments, preserving or re-creating their social circles from back home, real-estate agents and developers said.

Seven units at the Pendry Residences Park City in Utah were purchased by a group of friends from the same country club in San Diego, the developer said, while three were purchased by friends from Arizona. At Clear Creek Tahoe in Nevada, seven couples from Silicon Valley bought lots.