Fewer academics are gaining their first job at a university by the age of 30, while the number of older scholars has increased sharply.
These are among the findings of a report by the Higher Education Funding Council for England on the changing profile of people working in the sector over the past 15 years.
The study - Staff Employed at Hefce-funded HEIs - found that the number of academics under 30 at English universities declined from 12,205 in 1995-96 to 10,335 in 2010-11 despite overall staff levels growing by almost a third.
Overall, the proportion of academics under 30 fell from 14 per cent to 8 per cent in that 15-year period, while the proportion of over-sixties within the academy rose from 5 per cent to 9 per cent.
In terms of total numbers, the population of academics aged 60 or older almost trebled - rising from 3,955 in 1995-96 to 11,160 in 2010-11.
Most of those past the age of 60 (62 per cent) worked full-time, while 26 per cent were part-time and 12 per cent were doing very low levels of academic activity, the report said.
Geoff Whitty, the former director of the Institute of Education, University of London, said the changing age profile of the academy raised serious questions about the recruitment of "new blood" into the sector.
Last year's abolition of the default retirement age, coupled with increased financial worries caused by the recession, were likely to prompt academics to work longer, exacerbating the trend, said Professor Whitty, now professor of public sector policy and management at the University of Bath.
"I think there will be a temptation for academics to stay on because they can," he said.
"This will create problems in terms of freeing up funds to employ new blood."
However, Professor Whitty said the report, published last month, covered "a time when funding for universities increased significantly".
"You had the best of both worlds - an increase in people staying on longer but many more new people coming in," he said.
"The next report will show the impact of the recession and recent changes to the retirement age."
He suggested that universities needed to create more "exit routes" for older academics wishing to retire but who were keen to remain within the academic fold.
Establishing a "senior college" similar to the one created by the University of Toronto would allow retired academics to retain an "emeritus" status within an institution and pursue research interests, according to Professor Whitty.
"If you don't reach reader or professor - and most academics don't - then you can't become an emeritus professor. You need something similar for other retired staff," he said.
Professor Whitty added that it was important to avoid situations such as the "horror stories" from the US where eminent professors stay on but are then forced out by "capability procedures".
Michael MacNeil, head of higher education at the University and College Union, said changes to pensions would force many academics to work for longer. "I welcome the scrapping of the default retirement age, but we need to ensure that there are planned and supportive methods to assist staff," he said.
"We also need to ensure that changes to pensions do not deter staff from retiring at a time of their choosing, and the proposed increase in retirement age under (the sector's largest pension providers) to 68 runs contrary to this."
Mr MacNeil added that it was also necessary to create more "mechanisms" to allow early-career academics into the profession that did not simply rely on "low pay, job insecurity and worse terms and conditions".
You can't hang around for ever: The waiting game that drives away postdocs
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A lack of permanent positions is a key factor hampering young academics' careers, according to those who have chosen to leave the academy.
"My interest in policy issues was growing, but coupled to that was the fact that as a young postdoc, looking forward I couldn't see much opportunity for progress," said Rob Hardwick, formerly co-chair of the UK Research Staff Association.
Dr Hardwick worked as a post-doctoral researcher for almost five years, but is about to take up a policy role at the Biotechnology and Biological Sciences Research Council.
"It seems to be that you get a PhD and maybe a postdoc (position) or two, and at that point it becomes less clear where you can go," he said.
Experienced postdoctorates are often additionally disadvantaged by exceeding the eligibility criteria for early-career fellowships, while competing for an ever-scarcer supply of permanent positions, he added.
He suggested that offering alternative career options for senior academics who no longer had a passion for research could open up more jobs.
"If someone is not very research-productive, there is an argument to be made by the younger researchers who say, 'We're full of enthusiasm and ideas and we'd gladly take on some of that role'," Dr Hardwick said.
"You sometimes see senior researchers not being research-active any more ... (who settle) for doing basic teaching and not much more."
Angela Stokes, who until April worked as a postdoctoral researcher in cancer genetics at King's College London, said a move by funding bodies away from project grants and towards broader programme grants had also contributed to a reduction in postdoctoral positions.
"The general drop in postdocs has also meant that those left behind are supervising students more and doing less research of their own, with a knock-on effect on their publication record and ability to apply for fellowships," Dr Stokes said.
Jennifer Edwards, now a researcher at biopharmaceutical firm Eden Biodesign, said the academy's constant pressure to publish and to find funding contributed to a poor work-life balance, which is especially problematic for female postdocs who are considering starting families.
"It's not like I've got a nine-to-five job now; it takes dedication. But when I worked (in academia) I was in the lab at weekends, and sometimes overnight, because the work is all personal and if you don't do it, it doesn't get done.
"I compare that to the life I have now and I definitely wouldn't go back."
Source: Elizabeth Gibney
Growing older: How the academic population has changed since 1965
Source: Higher Education Funding Council for England