I believe I was around 9 years old when I stopped believing in Santa. I remember a friend at school telling everyone their parents had told them Santa was not real and so they kind of spoiled it for other kids.
My mom told me when I was 9. But I pretended on purpose thinking that if I acknowledged my disbelief than I wouldn't get any more presents. I dropped the act when I was a little bit older tho.
I can't remember what age I was when I stopped believing. I think I ruined the magic of Santa for my younger cousin though lol, I was 13 at the time and I was talking to his older brother who was 11 and I mentioned in front of my younger cousin who was 5 that Santa wasn't real. I had to quickly backtrack what I was saying to make sure he wouldn't get upset.
I had to say at my early teens, around 10 or 11 years old. I remembered one day at a very young age, I was out with the family, and we had visitors over, and they mentioned it while we were at a store and explained all about it and what age that santa stops