I was 10 and devastated. We were playing hide and seek and I squeezed behind a wardrobe in my mother's room. There I found things my sister and I had asked Santa to bring us. I felt horrible for asking for expensive stuff when I found out mother had been the one buying it. We were quite poor and to this day I don't how she did what she did with so little money.
Eight or so I think. It's hard to keep believing when you're the baby in a big family.
This has been a big topic in my house the past couple days because my 11-year-old is on the edge of disbelief and is testing all these theories- Tooth Fairy, Santa, Easter Bunny... Mind you, every time my kids ask if an entity is real, I have told them their whole lives that they don't exist. I roll my eyes and tell them that, obviously, these beings don't exist... that it has always been me. To which they consistently counter with all the reasons it can't possibly be me. The discussion is usually settled that way.
But, my daughter's latest take has been to intentionally not tell me when she loses a tooth, so she can prove that the tooth fairy only comes after she tells me. And, with Santa this year, she acknowledged she wanted a special pair of hiking boots identical to a pair her father bought her. She knew I couldn't get them because they were "too expensive," but she also ensured that I couldn't purchase the identical pair by not telling me what kind they were. After all, her father and I never talk.
My eight-year-old shared similar sentiments. "Mom, I know you're not Santa because you're cheap. If we get nice gifts, they couldn't be from you." (Yeah. He said that. Hmpf.)
So, my daughter woke up to the pair of hiking boots she wanted and my son got everything he asked for too. My son's still a firm believer because he knows I wouldn't buy him those gifts. My daughter remains a skeptic. She's about 99% certain Santa's real, but just in case she's wrong, she thanked me for the boots too.
It's such fun for them and you I know. When mine started asking I just said when you stop believing he stops coming. That got them a few more years before Santa stopped coming to our house and all the gifts were suddenly wrapped and under the tree. I always marked some of them as From Santa. I miss some of that fun stuff. I missed it all with my grandkids because they lived far away until the last few years but when they came back "home" I had moved across the country. Timing.
I still believe in Santa. Traditionally Santa was "Christkindel" - the Christ Child - Jesus. Our great Gift. Being a Christian its possible that if I am unable to believe in Santa I might not have enough imagination to believe in Christ.