I keep my tea in an airtight tin, it its original wrapper, in the pantry - in the kitchen I have a small tight tea tin which gets refilled when empty. Can't say just how long it would last. However, my educated guess says for quite awhile - especially if you were to use a food saver if you have one (I don't). Tea and coffee differ in that coffee has oils that can go off, and lose flavor; tea not so much. I treat my tea as I do leaf herbs - which is what it is after all. I know that the recommendation is to replace your herbs every year (or 6 months!), but I think that is just a ploy to get you to buy new herbs. If they are stored cool, dry, and airtight herbs will last longer than that - the sniff and taste test will tell you if they still have flavor. Treat tea the same way. Buying good tea to begin with is also a good idea - by good tea I mean loose leaf and not tea bags, which are generally filled with more finely cut leaves, with more cut surface to lose flavor from.
I will add that I probably have about 5 pounds of various teas at the moment. I drink a lot of tea, but even so some of what I have has been here awhile, with no noticeable loss of quality.
