VihtaVuori recommends a 10-year shelf life for their powders, but this is a pretty broad field. I've seen powder degrade after long-term storage, but I've also seen (and used) both powder and loaded ammunition that have been around far, far longer than this. Much of this comes down to storage conditions, but there are some other factors as well, that the handloader has no control over. There are a number of solvents used in powder production, as well as rinsing/washing steps that are intended to remove these same solvents after their job is done. Any variation in this, and the remainder of residual solvents or acids, is one such factor.
I know there are still quantities of reference powders, including Bullseye, that are over 120 years old now, which still test perfectly. I also have a fairly large quantity of 30 Carbine ammo that was loaded sometime after Korea, still canned, in stripper clips and in bandoliers that I bought from the DCM at Camp Perry nearly 20 years ago. Again, no issues with this ammo. But I have seen both commercially loaded ammo, handloads, and packaged powders that DID break down and had become useless in much shorter periods. Store it properly, check it for freshness (color and "finish", a fresh, noticeable ether smell, and the absence of the reddish "dust" or an unpleasant acrid smell) and it'll probably do just fine.
