I think around age 7 I figured it out over that year, so when I turned 8 (November) I was sure it was my mother. The clues I presented before that Christmas:
- The thank you notes from Santa were in her handwriting. My mother had very distinctive, artistic, clear handwriting.
- Santa had the same problems hearing what I asked for as she did. "You wanted a race car set? Ah.... Santa thought you said a set of erasers."
- The Christmases she was drunk (50/50), Santa didn't bring anything until she was sober, sometimes days late.
- She used the same wrapping paper. I mean, come on. It's not like she had only one roll, she used different paper for different people.
- Santa sometimes left price stickers for the local toy stores.
- She was a terrible liar once I established her rather simple tells.
So, after the usual "if you don't believe, you won't get anything from Saaantaaaa..." smarmyness, I spent some time wondering if I cared or not. At the last minute, I decided that I would have the best of both worlds: I set my alarm from 3am, and went into the living room, and hid under the couch. I dozed off under there, but was woken up my my mother sneaking stuff into my stockings. I made a mental note of every step she took, and when she went back to bed (awaiting me to wake her up), I got out and woke her up. I got presents. I got a little lecture about believing in Santa, but that was it.
Week later, I confessed I had seen her, and described the entire event. She was pretty heartbroken, but we did the Santa thing until I was 18 when she canceled Christmas weeks before her untimely death. I don't remember being depressed or disillusioned because by that point, I was simply proving my point, so my little 8 year old brain felt VERY clever.
Sadly, perhaps in denial, for years she still presented the "better be good" routine until I was about 14. She stopped when I said this:
"That's okay. I have a job now. I can buy what I need."