Over the last 10 years I have been heavy into Aro's. Some of my first blends from 15 years ago are still in good shape. I smoked a blend I stored 17 years ago last week, and it smoked and tasted just like it did 3 years ago, which I remember was what it tasted like 7 years ago.
Jud is correct, they do not age, (get better) but, stored correctly they should not get worse. Air is the enemy, keep that out and the casing will last. Evaporation needs to go somewhere and giving it no where to go keeps it in the baccy stored.
I Only use mason jars and make sure the lid is new, sealed tight and do not open and close it often. In fact my blending stock is all stored in mason jars, and it never seems to suffer.