We have lots of mature students across all of our courses - yes the majority of new students on undergraduate courses are 18-20 years old, and there will probably only be a small number of mature first year psychology students, but remember that your academic course is not the only way that you'll meet people.
If you're looking to make friends with other mature students, then there's lots of opportunities - from other students in your hall, to clubs and societies. All of our societies are open to students from all of our courses (which includes postgraduate and research courses).