Russ Chung once lived in a sizable Midwest home, but he recently downsized to a luxury one-bedroom rental in Midtown Manhattan just blocks from Central Park.

Now, rather than mowing a lawn, the 60-year-old higher education administrator spends his free time visiting museums and taking in New York's other cultural offerings.

"As you get older, there are only so many things you want to concentrate on. Apartment life lets you focus on things that matter and get rid of stuff that takes up a lot of time," said Chung. His building's concierge signs for his packages, and arranges for housecleaning.

Chung is one example of a subset of baby boomers who have become the fastest-growing group of renters across the nation. Since they tend to have more money to spend than their millennial counterparts, developers are actively figuring out how to lure them to into one of the luxury buildings sprouting up across the city.

Both boomers and millennials are flocking to areas like downtown Brooklyn, where a flurry of new full-services high-rises are springing up — and they sometimes compete over units, Citi Habitats agent Jason Burke told CNBC.

According to Burke, even though there is a glut of these new apartments, there is only a limited number in certain price ranges. Most people want to get in first when the developers are offering the best discounts, he said.

"The boomers are the biggest demographic that can afford it," he said. "But tech levels everything. We're seeing a lot of engineers come to New York, a lot of people in tech who don't work from an office."