When did you stop believing in Santa Claus?

I think i stopped believing in Santa Claus when i was probably 6, my grandfather always used to dress up like him every christmas until i was like.. 1O years old but at 6 years old i always had a thought in my head of where is my grandfather everytime Santa wanted to come to our house. so i just go to his room and found the Santa Claus outfit on the bed ready for him to put it on.  After that i knew he just dressed up like Santa to make me happy. Even when he knew i knew it was him he would still dress like it untill i turned 1O, just to put some spirit in that day, and i would always sit on him lap while he gives me presents :D that was such a great time <3 .. i Love my grandfather [':