“Between 2009 and 2013, the number of people ages 50 and older in federal prisons increased by 25 percent, making them the fastest-growing segment. The increase is not a result of an influx of older people into the prison system; rather, people serving lengthy sentences are aging behind bars. At the end of 2013, aging people comprised 26 percent of those held in minimum-security prisons, 23 percent in low-security prisons, and 33 percent in prison medical centers.”