I'm at Chester rather than York, but you shouldn't have any issues meeting mature students, particularly at 24. Unis will often put on social events, particularly in freshers week so different groups of students can connect. It's worth taking advantage of it. You would need to contact the accommodation team directly as they will have they're own way of managing incoming students. They may choose to put mature age students together, but it depends on the criteria. It didn't appear to be at Chester. I'm living in student halls, but have chosen a studio flat - I have disability needs as well as being in my forties, so living with others who are half my age was not going to be helpful. The building I'm in is primarily made up of 18-20 year olds, but I'm in a quiet area so its something of a compromise.