The longest I have tried is 3 months....I kept them in one of my empty herb bottles (or i guess like an asprin bottle) with cotton inside of it and they just germinated.
seeds in general, atleast from pine trees and whatnot, are built to last forever technically. They have everything contained in their shell to create the plant (aka sperm and egg) so they should be good when left in an airtight container until u need em..