I started to college after I retired, so I have some experience being the oldest in a class. Enjoy it! I found the instructors and the students to be very supportive. Having more life experience actually gave me an advantage with some of the subjects, but on the other hand, I found I could no longer memorize as well as I had 40+ years ago.
I was about 250 lbs and I had no problem fitting into anything. At my college we mostly had tables and chairs. The only bad experience I had was a hike in the pouring rain, with my geology class where I was the slowest person. It was not easy, but one of the other students (19 years old, and also overweight) and the instructor walked back with me.
My advice is to enjoy your college experience. It is so rewarding. BTW - it's fun to be driving with my husband through town and have a friend from college honk and wave.
Oh, yes - one more thing . . . I took a swing dance class to satisfy my last PE credit. I was the oldest and heaviest person in the class. It was fine. I teased some of the younger guys that they would be able to dance at their weddings with their grandmas.