There is a joke at Harvard University that the only things older than the fossils in its Museum of Natural History are the scholars in its classrooms.
Tenured faculty are not required to retire, and at least 180 Harvard professors - including nearly 20 per cent of those who teach undergraduates - are over 65.
Now for the first time, Harvard is offering incentives for its oldest academics to step down, clearing the way for younger replacements on lower salaries.
Some of those ushered out will not be replaced as part of a strategy to reduce not only the faculty's age, but also its size.
Although Harvard will not say how much the plan will save, the university lost per cent of its $37 billion (£23.1 billion) endowment when the recession began last year.
And while its finances seem to be recovering - some staff are even being promised modest pay rises this summer - the new scheme offers what administrators euphemistically call "faculty renewal".
The average age of Harvard's tenured undergraduate faculty is 56, but it is not necessarily the case that ageing scholars want to stick around for ever.
Harvard, unlike many of its rivals, has no formal means for them to step down while retaining such coveted perks as office space, assistants, library privileges and Harvard email addresses. Indeed, academics have been calling for a retirement plan for years.
The new plan, according to Michael Smith, undergraduate dean at Harvard, is "a flexible programme that is responsive to the many different goals that faculty have shared with us".
Tenured scholars who have taught for at least ten years and are 65 or older by 1 September 2010 are eligible. That description covers 1 of the 720 professors in the faculty of arts and sciences (18 per cent), plus more than 50 others in Harvard's medical, divinity, public health and education schools, which are making the retirement option available.
Academics, who have until 30 June to sign up, can choose to stop teaching at the end of this academic year and receive a one-year paid sabbatical, or wait two years and teach one out of every two semesters until then.
Alternatively, they can work for another four years, at their full salary for the first year and half salary for the next three, teaching full time and receiving full retirement benefits.
The generous terms are likely to pare the ranks of Harvard's oldest staff in what spokesman Jeff Neal called "a positive development for faculty considering retirement and the faculty of arts and sciences".
In addition to laying out a first-ever process for retirement, he said, the scheme "will also aid the faculty in academic planning - learning who plans to retire and when will help us better plan for the future".
The programme is voluntary and there are no estimates of how many staff will leave.
University officials said the savings, if any, would be long term: Harvard's undergraduate division alone still faces a $110 million budget shortfall for next year. So far, one 74-year-old professor of history has said he will accept the offer.
Full professors at Harvard earned an average of $192,600 last year, according to the American Association of University Professors, the largest academic union in the US.
'Stuff of legend'
Students' opinions about their long-serving faculty are mixed.
The Harvard Crimson student newspaper has argued that ageing professors should be encouraged to leave.
"While many older professors remain productive contributors to university life, others can no longer adequately fulfil their responsibilities," it said in a recent editorial.
"Older professors deserve our utmost respect and should be afforded the greatest dignity. However, they should not hold valuable faculty positions long after their time has passed. New generations require new blood."
But Johnny Bowman, president of the undergraduate council, said that older professors "are one of Harvard's greatest strengths".
"They're the stuff of legend for many undergraduates. In my experience, teaching ability does not differ between young and old professors," he said.
"The only discernible difference is the higher level of personal advice younger professors give. Luckily, there are 1,001 people at Harvard to turn to for advice, so I don't think that's an issue."
A legally enforced retirement age, under which professors at Harvard and other American universities were required to retire at the age of 70, was scrapped in 1994. When Harvard offered an early-retirement incentive programme this year to staff aged 55 or older who had worked there for ten years, 531 took up the offer.