Yes, the shutter design needs a certain amount of clearance from the inside of the tube to allow the front edge of the scoop to slide under and lift the shutter on insertion.
Whilst tight enough to keep most sizes of shot in I don’t think it would work with powder.
In use a single strap like mine (if it still had a strap) would be slung bandolier fashion over one shoulder with the pouch dangling nozzle down between the opposite kidney and hip. Gravity aids the feed. The extra strap on yours would be used to connect to the waist belt if it was flapping around.
As to age, impossible to be exact without markings except by condition of the leather.
