I'm not sure...
The oldest memory that I know for sure, I was 27 months old.
I know I have older memories than that.
I have at least two memories of being in my high chair, and the last time we tried putting my son in that very same chair, he was starting to outgrow it. So maybe around 18 months or so? I know I had teeth/molars.
I don't know when I learned to walk, I'd have to ask, but I remember running around a house at what was probably a Christmas party. I remember someone handing me one of those plastic candy canes that have candy inside. So that was either 11 months or 23. It was always a pretty foggy memory, so I want to say it was older.
Some time when I was 2, I remember laying in my parents' bed, trying to remember before I was born...but the furthest back I could go, was a memory of everything just being really dark, like a dark reddish brown. Possibly a memory of being in the womb?
...also, I'm going to assume that past-life memories don't count, because I have one from during/after the Civil War =)
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I'll brave the storm to come, for it surely looks like rain...