A version of this article first appeared in the CNBC Property Play newsletter with Diana Olick. Property Play covers new and evolving opportunities for the real estate investor, from individuals to venture capitalists, private equity funds, family offices, institutional investors and large public companies. Sign up to receive future editions, straight to your inbox.Senior living has long been a somewhat under-the-radar real estate play, with a somewhat unappealing reputation. But it’s on the edge of a boom — a baby boom, to be exact. More than 4 million boomers will hit 80 in the next five years, and occupancy at both active adult and assisted living communities is already rising fast. This comes as annual inventory growth in senior housing just dropped below 1%, the first time that’s happened since the National Investment Center for Seniors Housing and Care began tracking the metric in 2006. Ventas, a senior living real estate investment trust with a $31 billion market cap, is betting big on what CEO Deb Cafaro calls the longevity economy. “We’re buying billions of dollars a year in senior living, and we’re seeing returns in the sevens going in, with low to mid-teens, unlevered IRRs [internal rates of return], so there’s significant growth in assets, and we’re buying below replacement costs,” said Cafaro, who has been at the helm of the company for over 25 years. “I’ve never seen that combination of investment characteristics in my long career in real estate, and so we’re fully taking advantage of all of that.”Get Property Play directly to your inboxCNBC’s Property Play with Diana Olick covers new and evolving opportunities for the real estate investor, delivered weekly to your inbox.Subscribe here to get access today.Cafaro said growth in the senior living demand pool is expected to be 28% over the next five years. She called the demand tailwinds “incredibly strong and durable.””Think about 2000 in the real estate investment trust business — office was …