If your research shows that I would strongly urge you to publish it, because that’s a groundbreaking find.
In reality, the brain reaches its “full” size of 90% of your body mass around the age of 3. 75% at the age of 2 and 50% at the age of 1 and 25% at birth. Every source we have in Denmark suggests that the human brain starts forming memories around 5 months into the pregnancy.
It is access to these memories that aren’t always present, and that access seems to depend on repetition in ages 0-2 and language development beyond that.
However, if the brain was physically unable to form memories before the age of 5, well… small children wouldn’t be able to talk, walk or even breathe.
I have some recall of a few, vivid, subjective, first person, "umwelt"-style memories of events that I can date to before I was five.
These feel very different to my normal "episodic" memories.
Having spoken to my dad about the same subject before, he has some that he can place to about age 2 or 3.
I'm not arguing your point; granted, memory is reconstructive imaging from some engram and not a replay of some recording and I'm super convinced that our brains and mind go through several developmental stages that function quite differently.
I also find it super interesting that people with hyperthymesia usually have a perfect recall start date a bit after age 10.
My kid swears he remembers this one incident that my wife and I joke about, but what he remembers is the video of it. You physically don’t have the brain cells for long term memories until around age 5 which is why most childhood memories start around there.