The line between where the shower stall ends and the rest of the bathroom begins is subtle, just a gradual slope guiding water to a drain in the shower stall floor. The bathroom is Texas big — a 36-inch wide doorway and enough space in the middle of the floor for a wheelchair to easily do a 180.

Tasteful brushed metal grab bars are affixed to the walls by the shower stall and around the toilet. And hidden inside the walls are plenty of backing for easy installation of more bars.

In something prosaic like a bathroom, functionality often wins out over aesthetics. But the ground-floor facilities Ron and Carolyn Gruschow had built last year for their son, who has a variety of severe health problems, take huge pains to be attractive while also vastly more accessible than the average bathroom.

And as the Lima couple get up in years, the bathroom might eventually become theirs. “We figured down the road it’s big enough for us when we get old,” Ron Gruschow said.

America is getting older. Between 2000 and 2010, the block of population ages 55-64 grew by 50.3 percent, far faster than any other age range, according to a Brookings Institution study. The number of Americans ages 65 and up is expected to more than double from roughly 40 million today to nearly 90 million by 2050.

Those graying baby boomers represent a big potential home building and home renovation market. An analysis earlier this year by the Center for Housing Policy said that while estimates vary, some studies indicate that one in four older adults will likely end up with a mobility limitation that requires some kind of home modification. Those could range from the relatively cheap — such as handrails and bathroom grab bars — to roll-in showers or stair lifts that carry potential price tags of thousands of dollars.

Meanwhile, according to the center, the vast majority of older homeowners have indicated they want to stay in their homes for as long as possible.

“Aging in place” — construction or design features in a home that accommodate older residents — represents a still new and emerging field, said Michael Millner of Brighton home contractor Metro Legacy Homes LLC as he stood in a Pittsford bathroom renovated earlier this year with a wider doorway, a roll-in shower stall and space beneath the cabinet, all to accommodate a wheelchair.

The National Association of Home Builders started its Certified Aging in Place Specialist certification program for contractors with specialized training in the field in 2002. To date, there have been more than 4,000 graduates, according to the association. And 11 different firms belonging to the Rochester Home Builders’ Association have CAPS-certified staffers.

Done right, aging-in-place features are part of a universal design of a space that makes it usable by anybody, able bodied or not, Millner said.

The cost of incorporating design into a project such as a renovation can add as little as 5 percent to the cost, he said. “There’s more thought that goes into it” than a standard remodeling job, Millner said.

But the fact America is aging doesn’t automatically translate into a populace willing to accept and embrace that fact.

“Everybody is in denial,” said Peter Rees of Rees & Co. Inc., a Scottsville firm that specializes in bathroom and kitchen work and which built the Gruschow bathroom after, two years earlier, renovating an upstairs bathroom to be more accessible.

Less than 10 percent of his work involves aging-in-place projects. “I don’t think you could make a living just doing accessible bathrooms,” Rees said.

“A part of the problem is the concept needs to be more out there,” Millner said “There are alternatives to putting grandma in a home.”

Millner said universal design projects represents perhaps 25 percent of Metro Legacy’s business, though it is growing.

The Gruschow bathroom was part of an addition built on their Livingston County house in 2011 to accommodate son Dylan, giving him a ground-floor bathroom and bedroom as going up and down the stairs could be tremendously draining.

“I love it,” 20-year-old Dylan said. “It doesn’t take as much energy to get in, get a shower, and get out.”

“You’re not just trying to provide what someone needs,” Rees said. “You’re trying to give them something they like to be in.”