Higher undergraduate tuition fees may trigger a collapse in numbers of mature students in England, a study warns.
The report says the drop in applications for full-time places from mature students is almost double that from younger people.
The report for the National Union of Students and the million+ university group calls on the government to do more for mature students.
The government says financial worries should not deter anyone from study.
The report draws on figures from the admissions body UCAS which show that applications from people aged 21 or over for full-time degree courses starting in 2012-13 have fallen by 11.4% since last year.
This is compared with a drop of 6.6% from applicants aged 17 to 20.
Applications for university places from UK students fell by an average of 9% for this autumn, the start of higher undergraduate fees of up to £9,000 a year.
The report, Never too Late to Learn, says the drop in applications is evidence that higher undergraduate tuition fees may act as a deterrent to prospective mature students who tend to be debt averse.
The authors say fewer mature students would be a concern as they currently represent a fifth of all full-time undergraduates. A third of undergraduates start university for the first time when they are over 21 and more than half (57%) of these study full time.
A spokesman for the Department of Business Innovation and Skills said: "Mature students make a valuable contribution to higher education, bringing real-world experience, knowledge and skills into the classroom.
"New students do not have to pay upfront. Instead they can make manageable monthly repayments as graduates once they are in well paid work.
"Repayments are for a maximum of 30 years with any remaining balance written off after that time."
The report points out that mature students are less likely to have the usual set of A-level qualifications expected of school leavers. They are also more likely to study part-time and locally, to be from ethnic minorities and to have disabilities.
The study calls on the government to take into account the more complex financial circumstances of many prospective mature students when publicising the benefits of a degree.
It says the impact of the changes in fees and student support schemes on mature students should be carefully monitored.
In particular, it mentions that longer repayment periods for loans could be a particular problem for mature graduates if they are still having to pay them off as they near retirement.
Liam Burns, president of the National Union of Students said: "Mature students report financial hardship as one of the key challenges they face.
"We can't ignore the significant drop in full-time applications from mature applicants for the coming year, and we need to understand the reasons for this and prompt a change of direction in the government's approach."
Professor Patrick McGhee, chairman of million+ said: "This report is a timely reminder that social mobility is not just about young people .... contrary to popular perception university isn't just for 18 year olds with A-levels.
"This is something we should be proud of - it's a unique strength of our system - but it also means that we have a responsibility to preserve, protect and promote opportunities for people to study whatever their age, background and family, financial or work commitments."