10 years isn't old for primers, assuming decent storage conditions. I routinely buy various primers and powders at garage sales. You really don't know how those items have been stored but the price is nearly always so low that you aren't risking much. I use my bagain basement components just for plinking ammo but I don't recall any primer failures even with the caps that looked like they were swept off a bench and thrown in a bag.
So you bet, I would buy 10 year old primers but I would also expect a decent discount from the price of new components.