I considered the stories of Santa Clause and God to be pretty mind-blowing when they were presented as fact. So the realization that both were made up was kind of a return to sanity.
the santa claus/god realization could have been like 12 or 13, I don't remember exactly when I was told there was no santa, I'm estimating. I know I was three with the death thing, my parents remember me crying myself to sleep repeatedly moaning about it. of course they could be mistaken.
anyway, the ages were only there because I hadn't seen anyone referencing anything other than facts they heard recently. in reality nothing you've heard recently could be as earth shattering as the facts you learn when you're a kid that pull the veneer off your rosy fantasy world.