It takes courage to leave a secure job and return to the precarious world of full-time education as a mature student. Fionola Meredith reports.

Mature students are easy to spot on any university campus. But it's not simply their age that marks them out. After all, in Ireland you're a mature student if you're over 23 (or over 21 in the North). No, as any lecturer will tell you, mature students tend to be the ones that are noticeably more determined and disciplined than the majority of their youthful counterparts: turning up to tutorials on time, doing the required reading, handing in assignments promptly. These people have come to university the hard way, not merely following the well-trodden path straight from school, but often abandoning fat salaries or a comfortable retirement to immerse themselves in a penurious life of study.

Martin Sheen, star of hit TV show The West Wing and the iconic film Apocalypse Now, must be the most famous mature student in Ireland at the moment. He has enrolled as an arts undergraduate at the National University of Ireland (NUI) Galway, taking classes in English literature, philosophy and oceanography. At this stage in the new term, the 66-year-old actor will probably still be adjusting to the unique demands of campus life: queuing for the photocopier, drinking cheap beer at the students' union, agonising over the essay questions. Since his entry into the ivory tower, Sheen has not been available for interview. But several of his campus colleagues are happy to reflect on the pleasures and perils of life as a mature student.

Fellow sexagenarian and fresher at NUI Galway, Donncha Mac Sléimhne, is loving it all, after fulfilling a lifelong ambition to take a degree. The 61-year-old retired civil servant, who is studying philosophy, Latin, Spanish and IT, left school in 1964.

"Home circumstances meant that I wasn't able to go to university. I always had a yearning to go to college but I thought that doing a degree at night was too much - man cannot serve two masters. I retired at 60, and now my studies are like a full-time job. I find it very invigorating. I may have grey hair but my mind and spirit are young."

One of the distinctive qualities that mature students bring to their university studies is a wealth of life experience. Paddy McMenamin (52), also a student at NUI Galway, has a long history of self-education to draw on. Born in Belfast, he was interned at the age of 17, and spent six years in Long Kesh prison: "I had my formal education in the cages of the Kesh. I edited a small news sheet, learned to type, read thousands of books, learned Irish and developed a skill and love for writing."

But it wasn't until he took voluntary redundancy in 2003 from the automotive factory in Letterkenny where he had worked for 20 years that university started to look like a real possibility. He says: "To get the opportunity to go to university at this stage in life has been fantastic. I recently had lunch with my ex-boss in Letterkenny, and I told him I hated every day in the factory, but I've loved every day in college."

McMenamin believes that mature students in particular need a lot of support from their families. "I have received great encouragement from my partner and my (grown-up) children. In fact, my daughter is a mature student herself. At the same time as I started college, she was beginning an access course to do nursing. And my grand-daughter was starting her first year in school!"

Although university life is financially demanding for students of any age (with the possible exception of highly paid Hollywood actors), it must be especially difficult to abandon a well-paid job to embark on a degree course. Yet that's exactly what Aoife McNamara (25) from Westport, Co Mayo, did. She was in a full-time management position at Brown Thomas in Dublin, where she still works at weekends, before chucking it in to study commerce at NUI Galway. Why did she do it?

"Well, I wanted to get a better knowledge of business. But it's not just that. Retail is tough, very demanding. And although I loved my job, I started work far too young. I felt I'd given up all my freedom and fun too soon."

But it's not easy to move from the structured and fairly predictable world of work to the more fluid and intellectually demanding undergraduate lifestyle, with its emphasis on personal motivation and self-reliance. As an older student, it can be even harder to find your place among the hordes of noisy youngsters, giddy with their first taste of independence. Claire Bailey, mature student officer at Queen's University, Belfast, and a mature student herself, says it's easy to feel left out.

"When I started university, I was worried I was missing out on something. It was bugging me: I was paying the same money as everyone else, but I was left asking - what is this 'university experience' everyone talks about? There was no hub to pull you in, nothing to get you knocking on lecturers' doors and meeting people within the institution."

That's why Bailey was instrumental in setting up the "Discovering Queen's" pilot scheme, offering advice, guidance and social opportunities to adult returners. Simply meeting with other students in a similar situation is a great support, she adds.

As Ronan Murphy, mature student adviser at University College Dublin, says: "Mature students tend to bring their whole lives with them to university. The biggest hurdle is that even at 23, you can feel too old, and even more so if you're in your 40s."

A mother of two school-age children, Bailey knows from first-hand experience the challenges of balancing home life with student life. There's a measure of responsibility in many mature students' lives that is absent from the (relatively) carefree existence of the baseball-capped youngsters who surround them in lectures. After all, student mums don't have the option of plonking a tin of cold beans on the table for dinner, as their child-free teenage counterparts might do.

While the experience of a second chance at education may be personally and financially challenging, for some mature students, university life takes them on a journey they could never have imagined. An early hatred of mental arithmetic and a terror of being caned left Dr Myrtle Hill with enormous insecurities about her academic abilities. Having left school in Belfast aged 15, Hill had no intention of going on to higher education, instead taking a job as a clerk-typist. But when, in her 20s, she started an evening A-level course, Hill found learning as an adult to be an addictive experience.

"Not only history and literature but the world itself seemed more exciting and demanding, and it seemed imperative that I learned all I could." It wasn't an easy process - "I shed tears over essays and had to be physically forced to sit exams" - but after graduating with a first-class honours degree and a doctorate from Queen's, Hill eventually became director of the Centre for Women's Studies at the university. Not bad for someone who wasn't considered suitable material even to sit the 11-Plus exam.

The prospect of starting all over again as an undergraduate may be daunting, but for many the personal rewards make it all worthwhile.

"At 21, society expects you to have finished your degree," says Claire Bailey. "But if you have a few years' life experience when you enrol, you value university more. There's a purpose to it all."