Although all characters can wear regular armor for protection, only certain classes can wear light or heavy armor for advanced protection. The general rules for training armor talents and wearing more protective armor are as follows:
Privateer, Buccaneer, and Swashbuckler learn Light Armor at 5th level.
Privateer and Buccaneer advance to Heavy Armor at 10th level, and they are the only classes who may wear Heavy Armor.
Musketeers and Witch Doctors may spend a practice point to learn Light Armor (see the Privateer trainer) but they don't get any armor talent for free.