I am wondering if a Mage can wear Leather armor since it can be made without metal. Casting requirements mention hand gestures, so Leather should not restrict that really. I looked through all the Mage characters in the Adventure book, but none wore armor, so I wonder if I missed a rule somewhere, or maybe it is just assumed that they would not.
They can use leather, the rule say that studded leather is partially metal so leather is ok. Various NPCs perhaps doesn't have leather armour because they are made to look like "classic" mages (the stereotype mage usually have just a robe).