Olden green tea is a difficult tea to re-render well. The most it lost is not only the floral aroma but also the freshness in taste. If the condition is not so bad, most amino acids, the substance that give it the “umami” character, should still be there. To maximize what is left of the green tea, I increase the tea to water ratio and raise a very tiny bit the infusion temperature but reduce infuse time. The Yixing tea pot helps to reduce the bitterness of doing this and to give you a smoother texture. I also find that every single selection can be quite different in the degree of this modification and the condition of deterioration is also a variable factor.
As you have said, prevention of oldening is the best way to enjoy green tea. One way to do that is to store your finds well in a fridge in small batches, say 60~80 gram small packs, so you can always have a fresh batch at room temperature continuously throughout the year.
Hope this help, and pls let me know how you have experiment with your stock.
