One reason that young, aspiring academics find it so hard to land faculty jobs, many believe, is that older, established academics hang onto their positions well past traditional retirement age. Until 1993, many universities enforced mandatory faculty retirement at age 70, but a change in federal law  that went into effect on the last day of that year ended their ability to do that.
Since then, "a dramatic shift in retirement behavior" has taken place, according to a study  by Sharon Weinberg and Marc Scott of New York University in New York City. Published 15 July in Educational Researcher, the study examines a single university, but its conclusions appear likely to apply to others.
Before the legal change, only 11% of faculty members stayed on past age 70, "perhaps those with special arrangements," the authors suggest. Today, 60% "are expected" to stick around into their 70s and 15% into their 80s, they add. The study finds that professors' propensity to retire relates to their ability to "do meaningful work (and be well-compensated for doing so) outside of academe," notes an article about the study in Inside Higher Ed .
The faculty members most likely to retire are those who work in the target university's "highly esteemed professional schools [which have] strong ties to their high-paying fields of professional practice," writes Inside Higher Ed, quoting the study. "As such, faculty in these … three schools are afforded many opportunities to engage in external consulting and in other forms of affiliation with the practice side of their health care, legal, or business professions [and therefore] have opportunities for gainful employment following retirement."
The professors sticking around into their 70s and beyond, on the other hand, tend to be on the arts and science faculty and have fewer outside employment opportunities and earn less throughout their careers—and therefore have smaller pensions—than professional school faculty members.
Interestingly, today’s pattern of extended careers disproves a 1991 National Research Council report  that predicted "only a minimal impact" on faculty behavior from the change in the law. It appears that legislation intended to end discrimination against one group of workers, those middle-aged and older, has inadvertently increased the difficulties of another group, young workers struggling to get their careers underway.