If early memories depend on brain development, how can some people remember scenes clearly from a young age but others can't?

How is that some people can and do remember scenes from before they are ~3? If children can’t form explicit memories before they are ~3 then how come some people claim to remember things? Has that part of their brain just developed earlier for that particular person? If so, why? Why would some people’s brains develop that way earlier and other’s don’t? I know that we all learn to read and write at different times, is it just the same kind of thing? And why is that, anyway?

I know that I have a couple of memories that aren’t really memories- I’ve just been told the story so many times by other people I can picture it as if it’s a memory.

However, there are a couple of short scenes and flashes that no one in my family had ever talked about before but I remember them. I asked my mum why I was in the hospital when I was a baby because I remember the doctor picking me up, sitting me on a bed and using his stethoscope on me. She had never thought to tell me before but I had really bad gastro when I was 18 months old. That’s what it was from. So how come I could remember that? It wasn’t traumatic or scarring or shocking at all. I don’t remember the actual being sick or what they did to me or anything. Just that little bit with the doctor.