Right now, there are about five times as many people looking for work as there are jobs to be filled. But by 2018, a new study argues America could be facing the opposite problem — more jobs than there are people to fill them.

It comes down to demographics, argue Barry Bluestone and Mark Melnik of Northeastern University in a study sponsored by the MetLife Foundation and think tank Civic Ventures, with retiring Baby Boomers will leave a huge number job vacancies in their wake.

The two project that by 2018 there will be 14.6 million new nonfarm payroll jobs, plus some additional jobs in farming, family businesses and so on. Meantime, with no change in immigration policy or labor force participation rates, there will only be about 9.6 million workers available to fill those positions, leaving a gap of more than 5 million jobs that are vacant.

For the moment many older workers, having seen their net worth wither, have been hanging on to their jobs. In Southwest Michigan, for example, two nuclear power plants that employ many Baby-Boom generation workers told work force development agency Michigan Works! that they expected slots to open up. Michigan Works! is working on setting a training program for those jobs, but the plants then found that the workers weren’t retiring as quickly as expected.

“We know that there’s going to be a big demand — it’s looming out there,” said Todd Gustafson, executive director at Michigan Works! Southwest Michigan locations. But he doesn’t know when, exactly.

The study’s authors believe that in time, the problem won’t be older workers hanging on to their jobs past retirement age, but older workers not staying in the labor force long enough.

“Not only will there be jobs for these experienced workers to fill, but the nation will absolutely need older workers to step up and take them,” they write.