Clark County’s 90-plus population has nearly doubled in the past 10 years, keeping pace with the nation’s increasing longevity.Some 2,245 county residents reported they were 90 or older in the 2010 census, up 84.9 percent from 2000.About 71.7 percent of people in that age group are women.Those who are 90 and older make up about 5 percent of the 65-plus population and less than 1 percent of the overall population.Expectations for longer life among the county’s senior population prompted county officials to form an aging readiness task force earlier this year. The task force made recommendations to help planners prepare for the infrastructure and services that will be needed to accommodate a senior population projected to double by 2030.WASHINGTON — The rolls of America’s oldest old are surging: Nearly 2 million now are 90 or older, nearly triple their numbers of just three decades ago.It’s not all good news. They’re more likely than the merely elderly to live in poverty and to have disabilities, creating a new challenge to already strained retiree income and health care programs.First-ever census data on the 90-plus population highlight America’s ever-increasing life spans, which are redefining what it means to be old.Joined by graying baby boomers, the oldest old are projected to increase from 1.9 million to 8.7 million by midcentury — making up 2 percent of the total U.S. population and one in 10 older Americans. That’s a big change from over a century ago, when fewer than 100,000 people reached 90.Demographers attribute the increases mostly to better nutrition and advances in medical care. Still, the longer life spans present additional risks for disabilities and chronic conditions such as arthritis, diabetes and Alzheimer’s disease.