The U.S. census has released data showing a 15 percent increase in the population age 65 and over. That amounts to more than 40 million Americas. Western states like Arizona, Colorado, Nevada and New Mexico had the fastest growth of older residents. A number of counties across the southwest experienced a more than 70 percent increase in the number of seniors. Scottsdale, Arizona is the country's oldest city, where 20 percent of the population is over age 65. The census bureau attributes most of this growth to people who move south after retirement. As a whole, the nation is getting older. People age 65 and over account for 13 percent of the overall population.