The Ucas website has a section dedicated solely to mature students; specifically those who are over 21 in England (over 20 in Scotland). There are lots of reasons mature students decide to study, but many say their objectives are either to improve their career prospects or because they are deeply interested in the subject.
Higher education institutions including universities want to widen participation and one way of doing that is to encourage more mature students. They are more likely to enjoy their subjects and knuckle down because they are studying by choice rather than because it is expected of them by parents. Some may have had good careers already and so understand the frustrations that can come from dead end jobs as a result of a lack of qualifications.
Ucas offers guidance about choosing the right course and also gives careers advice about how different subjects are regarded in the workplace. The Open University prospectus offers all sorts of advice about their subjects as well as the careers they can lead to. It also covers the entry routes offered to students and a lack of qualifications does not necessarily exclude mature students.