Do other young girls experiment at sleepovers

I always wanted this to happen when I was younger. I used to finger myself and imagine I was doing it with one of my friends but I was too scared to ever ask anyone. Nobody ever invited me to sleepovers. Then when I was 13 my family moved and I went to a new school. I made a lot of friends and the first time I went to a girls birthday sleepover was when it finally happened. We were all staying in the birthday girls room and birthday girl wanted no time that night getting everyone to undress and finger each other. After a while we began licking each other and watching each other. There were many orgasms that night. It was the best night of my life. For the next two years it happened at every sleepover. 

Why did it stop at 15?