It's a guessing game, highly dependent on the brand, the blend, the source, the leaf, the processing, the tins or jarring or mylar bags, the storage, the climate, and your astrological sign. (Not that last.)
I don't age anything on purpose. I just buy more tobacco than I smoke so the rest of it ages.
I'd say, with Virginia and Va/Per you might get improvement up to about five years, and properly stored, that could last ten or fifteen.
Burley doesn't improve much, they say, but it keeps as well as any leaf.
The aromatic flavoring doesn't keep so well, a few years, but if it is applied to quality Virginia, that might improve while the flavoring fades.
I say, smoke it as soon as you can, and the blends you don't get around to smoking will age themselves. Seize the day.