There is no solid evidence that teaching reading early is advantageous, and in fact there is evidence that it can be damaging. No one really knows why exactly, but there are several theories ranging from discouraging other types of play and interaction, to the difficulty turning them off of reading later on.

>it's "how soon does this kid have the tool to satisfy their natural curiosity about things that require more than someone telling them about it?"

I don't think that's true at all, an average 4-7 year old who can read, cannot read to a level where they can learn topics complex enough that they "require more than someone telling them about it."

A kid who learns to read at 7 will catch up to the kid who learned at 4, so that by the time they are ready to teach themselves on their own through reading, there won't be a difference.

https://deyproject.files.wordpress.com/2015/01/readinginkind...