Realize that properly stored, gunpowder can last a long, long time. Also realize that powder prices, and availability is far from normal. Find someone that wants it, and sell it depend it on it condition. Do not open it until then.
I guess as late as early 80's. 10 years ago I picked up a can of Dupont powder in a can approx. 5-6 lbs and the bottom completely fell out of it, rusted thru and the powder was a brown dust. This was even stored inside home all its life. I have used a lot of older powder and that is the only time I seen that happen.