One of my earliest memories is the sunlight slanting across our living-room floor in our old house. We had a yellow-ish hardwood floor, with little nicks and scratches in it from where we'd moved furniture, and me and my brother had played with our toys. I remember lying flat on my stomach on the floor, tracing those scratches with my fingernail. I don't know where in the timeline of my memories this fits in, but I don't think I could have been more than four or five.
As for my character's earliest memory.... Let's pick Akane.
Akane is probably five years old. I say "probably", because she doesn't know, and neither does anyone else. If asked, her only reply will be "..." - which is, honestly, her reply to most questions. Her name probably isn't even Akane. But yes, she is five years old, and her earliest memory is from just a few weeks ago - because her earliest memory is this:
She remembers a forest, and a clearing in that forest, and she remembers the blood. She remembers bad men with swords, and screaming, and more blood. Beyond that, things are very hazy.
But she remembers the river, and the man who gave her her name.
(Hi, read Grassblades - it's got a semi-mute little girl, a grumpy swordsman being the awkwardest adoptive-dad, and lots and lots of blood)