Two factors drive the housing market: the economy and demographics. At the moment, both are trending in favor of realtors and builders. Industry experts are forecasting a stronger housing market for 2015, with millennials and boomers being major players.

The National Association of Realtors predicts a 3 percent growth in GDP for next year and a 3 percent increase in household income. Together these economic improvements would help unleash the pent-up demand for home purchases. In particular, they might give millennials the boost they have been looking for to transition from renters or "boomerang kids" to homeowners.

NAR has already dubbed 2015 "The Year of the First-Time Home Buyer," with millennials expected to have the greatest impact on sales.

"In 2015, increases in employment opportunities will empower younger buyers to return to the market and fuel the continued housing recovery," says Jonathan Smoke, chief economist for Realtor.com. "If access to credit improves, we could see substantially larger numbers of young buyers in the market."

In addition to improved prospects, or perhaps because of them, millennials have also started to reach the age when they think about getting married or living with a partner and starting a family.

Amy Hoak, a reporter for MarketWatch, relates that in a recent survey of millennials: "86 percent said the primary trigger for purchasing a home was because they had a change in their household size or were anticipating one." Moreover, 32 percent said they were planning to increase their family size, and 18 percent said their family size had already increased.

Another motivator may be that millennials are tending to stick with their jobs and thus their present locations. A recent Washington Post article reports that, according to data from the U.S. Census Bureau and Bureau of Labor Statistics, "Millennials seem to be sticking with their jobs longer than their counterparts did a decade ago."

Of course, this applies only to those fortunate enough to have found jobs. Between 8 and 12 percent of millennials are currently unemployed, which may explain why so many who are employed are sticking with their current jobs.

Curiously, that other demographic behemoth, the baby boomer generation, is trending in the other direction. Analysis of Census Bureau data conducted by the NAR indicates that with more boomers looking to work beyond the traditional retirement age of 65, some boomers are pulling up stakes and moving to greener pastures.

"Metro areas with a lower cost of living and sunnier weather are poised to see an increased number of baby boomers moving in and buying a home as some delay retirement and remain participants in the labor market," the NAR researchers found.

Some areas have seen increases of nearly 20 percent. Among the top 10 metro areas working boomers are finding attractive are Boise, Idaho; Raleigh, North Carolina; Orlando, Florida; Albuquerque, New Mexico; Denver, Colorado; and Tucson and Phoenix, Arizona.

On the other hand, most boomers who are retired or thinking about retirement plan to stay put. Custom Home reports that The Demand Institute's Housing and Community Survey reveals that nearly two-thirds of boomers (63 percent) plan to stay where they live now when they retire.

Contrary to the long-held view that boomers will want to sell their family-sized homes and downsize in retirement, nearly half (46 percent) said they would like a nicer home with more space.

That finding tracks with consumer behavior trends identified by marketing researchers at Moen. They found that most boomers are choosing to "lifesize" rather than downsize. Boomers, they say, consider their homes a haven and would rather invest to make them more supportive for aging in place than relocate to a senior living community.

"Today, boomer empty-nesters are opting to invest in their homes to create their perfect environment that's both safe and stylish," said Jack Suvak, senior director of consumer and market insights for Moen.

If boomers decide to stay put, whose homes will millennials buy? That's a question that might keep a few builders up at night.