Why don't i like hanging out with my friends that much? is this normal?

I'm 18 too and a little bit of a homebody. I wouldn't worry about it. If your sister is younger than you, then she's really lucky to have a big sister who actually WANTS to hang out with her, and if she's older than you, you are lucky to have a sister who wants to hang out with you. I wish I had that relationship with my older sister. We will get there, but just appreciate your life right now and do whatever the hell you want....cause HEY! WE'RE DONE WITH HIGH SCHOOL!!