The model works fine, I don't know why this would be other than you don't have the correct version of Optifine.

That's what the normal guardian model is. All you would need to do for this is download my Prickly Guardians pack, delete the "elder_guardian.jem" file, duplicate the "guardian.jem" file, and rename it "elder_guardian.jem". Thiss will take the guardian's model (The same thing but with one eye and one tail) and apply it to the elder guardian. Hope this helps!

2 Eyes ;-;