My cousin went to Canterbury Christ Church University to study Nursing, she was a mature student, she started at like 22 or so I think. A lot of his friends from the course seemed to be mature students...
Regardless, it shouldn't be a problem. There's mature students on every course in every university, in many unis there's also mature student societies to make friends, and it's not as if the younger students care about your age, so it shouldn't be a problem.