I'm slightly embarrassed. I actually thought I had been around 6 or 7 years old, but now found out that I had been nine. I found it out by "altruistically" wishing for world peace, which the all-powerful Santa should have been able to provide. I only got a game called Game of Peace (Looking it up right now, I found out that it was published in 1993, so I can't have been younger than 9 at the time). That's when I definitely stopped believing (Although my parents could have probably convinced me that Santa existed, but wasn't all-powerful, if they had bothered).