But now the under-25s are the fastest-growing age group at the institution, which pioneered distance learning. Thousands of students now choose to study at home through the OU, not because they lack the grades to go to a conventional university but because they think a full-time degree will be too expensive. Faced with dwindling university grants and the necessity of having to take out loans to support themselves at college, they choose these part-time undergraduate programmes instead. This way, they know they can earn while they learn.
This year 4,173 under-25s enrolled for degree-level OU courses - compared with 2,762 students last year. Although the group still forms a small proportion of the university's 140,000 students, its numbers are rising fast. And a recent survey of its members revealed that more than half had chosen this option for financial reasons.
With all the main political parties now keen to find ways of making graduates repay a greater proportion of the cost of their studies, more and more young people are likely to follow the OU path, according to its spokeswoman, Annette Mathias.
"We may be witnessing the beginning of a trend where 18- and 19-year- olds make a conscious decision to join the OU rather than a conventional university," she says.
David Booth, 19, from Pontefract, joined the OU's first-level degree course in computing this year.
"I opted for the OU because I simply could not afford to support myself at a conventional university," he says.
David is unemployed at the moment but hopes to find work as a trainee in a computer firm to pay his OU fees.
Students who choose OU must pay about pounds 3,000 in fees before they can gain a degree and they are not eligible for mandatory grants. But unlike conventional university courses, theirs is designed to allow them to work at the same time. They can also save money on rent by staying at home.
The other important reason why so many under-25s are opting for the OU is that they can store up some work experience even as they study for a degree. Sharon Power, 19, joined the OU last year and works as a secretary. She hopes to graduate in psychology but feels her present work experience will stand her in good stead if anything should go wrong.
"A lot of graduates fail to get jobs because they lack work experience. And if at the end of three years they don't pass they have nothing to fall back upon," she says.
`I never wanted to go to university'
Jane Bradley's A-level grades would have got her into a conventional university but she opted for the Open University instead.
With an A, C, D and E she was offered a place to read English language and social science at the College of Ripon and York St John, but she turned it down. Now she works as a shop assistant in Sheffield and studies in her spare time for an OU first-level degree course in social sciences.
Jane, who joined the OU in February, passed her A-levels in 1994. "I never really wanted to go to university," she says. "You don't always get a job after you graduate. Employers don't want you if you have no work experience, so I would rather get an OU degree and get some work experience while I'm at it."
She relished neither the prospect of being a graduate without any work experience to fall back upon nor the expense of getting a degree at a conventional university.
"The OU fees are not exactly cheap but considering the amount I would have had to pay if I had been away at university, it is not that much at all."
She lives at home at her parents' garden centre and saves on rent, and her job pays for most of her OU course fees. The rest is paid by her parents. She loves the programme, though she finds it quite demanding, and plans to join the police force in six years' time when she gets her degree.
"It involves a lot of reading and you have to be dedicated to keep at it," she says. "But there is always your tutor to help you if you get stuck. I find it challenging."