A growing proportion of the nation's professors are at the same point in their career: still working, but with the end of their careers in sight. Their tendency to remain on the job as long as their work is enjoyable--or, during economic downturns, long enough to make sure they have enough money to live on in retirement--has led the professoriate to a crucial juncture. Amid an aging American work force, the graying of college faculties is particularly notable. According to data from the Bureau of Labor Statistics, the number of professors ages 65 and up has more than doubled between 2000 and 2011. Colleges have been talking about an impending mass exodus of baby-boomer professors for at least the past decade, but it hasn't occurred yet because people in their 60s, in particular, aren't ready to retire. But even with the preponderance of older faculty in academe, experts say that widespread retirements aren't imminent, but instead will most likely take place in spurts over the next 10 years or so as more professors reach age 70. In the meantime, the challenges of an aging work force are especially salient for colleges. Faculty can retire at will (a perk that began with the end of mandatory retirement in 1994), and young Ph.D.'s are waiting in the wings for jobs. Institutions are also struggling to manage faculty renewal at a time when the position left behind by a retired faculty member might be lost to budget cuts. Older professors understand what's at stake. But at the same time, they have managed to craft professional and personal lives that they're not ready to walk away from. And some administrators, who are themselves often in the same age bracket as the faculty in question, can relate. Yet their task of preparing for the next generation, while managing the previous one, remains. Data on faculty ages collected by "The Chronicle" provides a window into how the shifting demographics of professors is playing out similarly at all types of colleges across the nation. The problem is more pronounced at some places, particularly at elite research institutions like Cornell University, where senior professors often have particular freedom to shape their academic pursuits to fit their interests. At other kinds of institutions where the workload isn't as flexible, studies have shown, faculty members are more inclined to retire.