Is there any way I can go back to high school?

I never really had a school life. I was always the quiet one in the corner. I was in special ed classes for the majority of my school years. It wasn't until my senior year that I took Introduction to Chemistry and was overjoyed by the methods of learning facts about the physical world. After graduation I tried community college but couldn't handle all the required prerequisites so dropped out, and my guess is college classes aren't as easy and fun as high school classes. So I guess what I'm wondering is if I could enroll in high school classes even though I already have my high school diploma. I'm 21 but I think I look young for my age so it probably wouldn't be so awkward for the students who have not yet graduated. I'd just love so much to make up for all the fun learning that I missed.