Some parts require more math than probably the general audience will be able to grasp but if they gloss over those sections they could still get the gist of what follows.
I think I’d rephrase it as “quite approachable for a talented high schooler / someone with knowledge in undergraduate mathematics”
Why assume that ? Isn't the whole point of high school to provide a basic foundation of knowledge that everyone should have ?
The parent comment said “quite approachable for the non-expert” not “quite approachable for the uneducated”.
Personally I did study mathematical logic in the University a little bit, but it was 20 years ago and I don't think I remember much about it past what all undergraduates are taught.
Also, about half of the book can be read without any Math background.
But yeah, it is a very good book, one of its kind. I wish there were more accompanying books written in similar fashion.