A mature student is defined as anyone 21 or over (20 or over in Scotland) by the time their course starts. Some universities set the age at 25. Sometimes, universities and colleges will waive formal qualifications for mature students, but others may demand almost the same qualifications as they would from an 18-year-old.
We advise that you talk to universities and colleges direct before applying. You can check the mature students section of this website for more information.