Lori, has he read Euclid's Elements?
The Geometry you mentioned is more nomenclature, ie labelling, not Geometry. The angle thing you mentioned is more to train slower kids to think about angles and what they mean. You son already intellectually grasps the concepts of geometric equivalence so his visual comparison skills are not needed to learn this idea.
The nice thing about Elements is that it is self-contained book of study - and introduces the idea of abstract thinking and rigor to young minds. And the language is quite quaint so given his ear for the nostalgiacal, he should get a kick out of it.
http://aleph0.clarku.edu/~djoyce/java/elements/toc.html
One suggestion is that should he like Elements, then it can serve as an introduction to learn either Latin or Greek by reading it in those languages.
