Is it the Level 3?
My only experience is that my daughter is doing a different subject extended diploma at level 3. In her case, it is very vocational, and could - in theory - lead to her being able to work. In reality, though, there are so few opportunities out there, that she is going to have to extend her theoretical knowledge, maturity and practical expertise with a degree.
Her course would also be expected to be mainly 16 year olds but she went to a competitive college and, actually, out of the original starters of 60, about half were over 20. Also, as the year as progressed about 15 have left - not able to keep up with the work required or found that the course is just not for them - and most of those were the younger ones.
I asked her about bitchyness. She reckons as many of the older students are as bad as the younger and doesn't think age matters (although that surprised her!). She just gets her head down and works hard and avoids them - her best friends at college are nothing like it and you don't get huge amounts of social time to spend together anyway.
Also, do not under estimate the work you are likely to need to do. It may be one day a week of lectures (hers is 2.5 days a week) but there will be a lot of work outside the course on assignments. For higher grades, my daughter has been putting in at least 15-20 hours a week, on top of a two and a half day course attendance. She is aiming for distinctions.
If you have social anxiety, maybe CBT could help outside of college.
Good luck!