I think there is a set of skills that are really worth learning early. When it actually makes a difference to be "native". Like learning a language, playing an instrument or technical sport like let's say skiing or swimming. I'm fluent in English now but will never sound like a native. I swim several time per week but I'll never be as efficient as if I started at 6. On another hand I started skiing at 4 and I've been doing great in this sport.

For coding, I think the author wants to emphazise the fact that the code syntax and the logic are different things. Syntax is easy to pick up at any age with a bit of perseverance. Kids can practice their analysis skills and logic at a young age but that doesn't require any coding.