If someone writes a symphony today, does it have to wait a certain amount of time before it can be catagorized as "classical?" If someone writes a country and western song does it have to wait a certain amount of time before it can become a country and western song? I could go on and on. The point is, folk music is a catagory of music. It's not how old it is. If this is the case, Mozart's music is all folk music, not classical.