I went back to college at 24, as a junior, after four years away, and already I felt at least a generation older than the youngsters in the room around me, who had never been out on their own or supported themselves. It’s not an unbridgeable gap, but you do have to expect to find your common ground differently from the way you did when you and your classmates were all in the same age group. Don’t expect too much in the way of a social life with classmates.
The first couple of classes of the term are usually about orientation and ground rules and such—overview of the course, basis of grading, etc. This is partly just because the composition of the class takes a week or two to settle down while students are still dropping and adding. Don’t let the administrative stuff turn you off your coursework. It’ll get better. Do your assignments, dig into your studies, and enjoy the excitement of the learning process.
When I retired from full-time work, I started attending classes at a junior college just for fun. I was two generations older than the students (but I wasn’t the oldest student!). One of the instructors was born the year I got married. Nevertheless I managed to establish friendly contacts with several fellow students, and we got along just fine. They were very accepting of me, and I didn’t expect them to be more mature than the average 19-year-old.