A rarely discussed topic in academe: the senior-citizen faculty

A few years ago, when I was in California, a friend retired the moment he became eligible for the reason that he did not want to stand in the way of a younger person hoping for a teaching career.  And, yes, his replacement was fresh out of grad school.
It is quite a tough challenge: on the one hand, we gain from the immense knowledge-base that a senior faculty brings.  On the other hand, every single day past retirement is another day that a PhD remains off the tenure-track.  Further, the compensation package of a senior faculty typically is far more than that of a new hire. 

The slowing of retirement since the end of mandatory retirement under federal law, in 1994, has added another growing problem to the job-market mix. At the University of Pennsylvania—the only place for which I can get more or less exact and timely data—we have gone from having no faculty members over 70 in the School of Arts and Sciences, 15 years ago, to 28, or 7.3 percent of the 383 tenured faculty members, in 2010. And the median age of tenured faculty members has risen to 55.
Seven-plus percent is a substantial proportion, especially since each of those senior citizens is arguably blocking at least two assistant-professor slots. Penn could probably add upward of 40 new assistant professors in the School of Arts and Sciences, without significantly increasing its instructional budget, if everyone over 70 retired. (Whether Penn's administrators would actually do that much hiring is, of course, an entirely different matter.)

Anyway, the author, a professor of English and Education at Penn, notes that in the context of the harsh realities of (un)employment in the humanities.  Yes, not a new topic to this blog! And, I should note that the retirement factor is simply one of the many issues that are discussed in that essay. 
The essayist concludes on the following note:

I would much prefer to define our current job-market difficulties as a problem in underdemand rather than oversupply. The facts, however, cannot be denied. After a generation of dithering, we need to act decisively to minimize the damage that our practices are inflicting on thousands of talented young women and men whose aspirations and idealism are jeopardized by our institutional inertia as well as by our laissez-faire, wishful thinking that the job market will simply take care of itself. If we should have learned one lesson from the current financial crisis, it is that all markets need vigilant oversight.