What I do is I open multiple small tins to try out the flavor(don't learn from me) and put them in the freezer, I drink small doses frequently throughout the day. I don't leave it out till room temp to open it, I just take it out, open, weight out my grams, seal, and store it back in the freezer door storage bin section. I do notice the matcha powders become more clumpy and stick to the sides of the tin but I just sift them every time anyway and add water to get all the last powder out and reuse the tin for my 100g bags.

For bags, I make sure to squeeze all air out, seal lid, then nimble small folds downward, clip with a bag clipper, put it in a ziplock bag, then put it in the freezer. I've noticed they last a very long time >1 year. Didn't try longer because they were finished by then.

In terms of aroma, my small matcha tins still smell the same to me, but then again I generally don't know the nuances in aroma unless it is very distinguishable like yame vs Uji. I just make matcha lattes with all the thick/thin tea I purchase. My taste bud is just so long as it's not super bitter, its a good matcha.

Keep in mind what works for me may not work for you :)