My child is nine and has never seen any of this. Where do we start?

At their own age band. Question Years or Builder Years, not the Crayon Years books.

Each band is written to assume the one below it without requiring it, so a nine-year-old starting fresh is not missing anything. Handing an older child a coloring book aimed at four-year-olds mostly teaches them that this subject is for babies, which is the opposite of what we want.

If you genuinely cannot tell, go one band below where you think they are. Being early with the concept is the point of this project. Being early with the difficulty is just a bad afternoon.