My younger sister was so traumatized that she wouldn't even let her children believe in the first place. I give her the stink eye when one of her kids will pipe up. I don't remember what age I was to be honest. My daughter figured it out in 5th grade (10) and I reminded her that Santa remembers to make things even so if she blows if for her younger brother (7), she'd blow it for her too. My son is way into Santa, the Elf on the Shelf so I hope it hangs on for a few more years. It's fun to watch him.