I found out around age 6, and it didn't exactly scar me or anything. My mom told me the truth the first time I asked outright if he was real. I told my son Santa was real when he was little. He didn't buy it. He was 4 and he told me "that's impossible". I asked him where the presents come from and he said "you".
So I agreed. I certainly wasn't going to try to convince him.
When he started Kindergarten at 6, he wavered a little because all the other kids believed it. He told me he didn't see how any of that could really happen, and I told him it was just a story to make the holidays fun for kids.
I don't see anything wrong with letting your kids enjoy thinking it's true for a couple of years. But so many parents try to squash their kid's reasoning when they are figuring it out.
I never told him the mall Santa's were helpers, the reindeer ate special dust so they could fly etc. Basically, I let him question and reason it out and agreed with him when he reached the truth. I guess it may seem mean to some people to lie to their kids, but if you think you will Never lie to your kid, I doubt you have a teenager yet.
I think the santa story and discovering the truth can be beneficial to young kids. Especially if you are raising a kid without religion, as I am. It's a chance to see that a Lot of people, what seems like "everybody" to them, can believe something that isn't true. That you have to think about things , question, and see what makes sense.
If they think the Santa story sounds unbelievable, they won't be likely to believe in a magic talking snake, angels, and so on.