A whopping 53.7% of Indiana's licensed registered nurses are 45 and older. An additional quarter are older than 55, and that paves the way for what some experts predict will be a critical shortage of nurses in the coming years as millions of baby boomer nurses retire. The phenomenon of older nurses calling it quits is already hitting the state. Nearly 52% of registered nurses 55 to 64 years old say they will retire in the next four to nine years, according to a survey produced by the Indiana Center for Health Workforce Studies and Bowen Research Center at Indiana University School of Medicine. In 2011 alone, there will be 2,281 openings for registered nurses, according to the Indiana Department of Workforce Development.