Most manufacturers guarantee that their ammunition will last at least a decade. That said, ammunition can easily last more than 10 years if stored under ideal conditions. There are countless stories of surplus military ammunition being used many decades after its manufacture. Proper ammunition storage is crucial for the firearms you rely on in an emergency, such as your concealed firearm.
A weapon like that could go for years without being fired. Although most manufacturers recommend not using ammunition older than ten years, prevention is better than cure. After a few years, he uses those old rounds at the first opportunity, maybe practicing a little at the shooting range. The useful life of munitions depends mainly on their state of conservation.
On average, ammunition can last at least ten years. However, your weapon may still be able to fire with the same ammunition even after a decade, as long as it is stored under ideal conditions. Once again, the useful life of ammunition is theoretical. As long as your ammunition is safely stored and protected from moisture or sudden temperature changes, you should be able to keep it for decades.
Ammunition manufacturers limit their liability exposure by being more conservative in their estimation of useful life (not to mention selling more boxes of ammunition by encouraging more frequent purchases). You'll need to store your ammo in ammunition cans or sealed storage containers with air conditioning to keep out moisture. Ammunition companies are pushing a conservative message, probably because they don't want responsibility if it doesn't shoot (and, hey, they'd like to sell more ammunition).