Hi there!
Reading this thread makes me think what do you guys consider a "very mature student."
I'm 50 and I will start a degree with a foundation year next month. When I was in my 20s I certainly thought that a 50 years old person was "very mature", and yet, here I am now, and I have no idea what "mature" is when it comes to deal with people. In some ways, I still feel a young lady, in other ways, I feel much older than 50. It's a fact that we may not be as good as we used to be in some aspects (I notice that I take longer to do some things, especially in maths), however, I also notice I can produce much richer material, I think this may be due to the experience life provides along the years, this is the main difference I feel. But I never saw myself as unable to blend in with other people despite their age. And that hasn't changed over the years.
Last year I decided to take English and Maths Higher GCSEs as an adult student. I was really terrified, not only because I was returning to the classroom after so many years, but also because English is not my first language and I thought my communication skills could hold me back, both in the subjects I was taking and the social interaction. I'm a fairly extroverted person, and what I found out is that I was able to connect with older students, younger students, some British, and some from other nationalities, it didn't really matter in fact. It all depends on our own efforts to try to interact with others and their own personality traits. Some would be very receptive and friendly while others may not that open-minded. But when you look back, this was already the case when we were younger, trying to find our peers in high school.
All this to say that we shouldn't be worried, as long as we try to fit in, we will eventually be able to find at least a handful of people we get along with really well, and that should be enough; I don't think this has nothing to do with their ages. Some of the friends I made while taking my GCSEs were less than half my age.