If they were canned following current safe guidelines (I'm thinking especially of low-acid pressure canned foods) and the seals are sound, they'll be perfectly safe to eat indefinitely.
Things properly canned don't suddenly become "unsafe." What does happen over time is flavors change, textures soften, colors darken or fade through oxidation. So when the product is no longer appealing or tastes flat, that's when to throw it away.
I just had to comment on this... My grandmother passed away and I got to clean out her cellar (oh-joy!) She had canned goods down there and I am POSITIVE that the cure for cancer was in one of those jars! The oldest date I could read was from the 1960's (way before I was born!) Some of the lids had even rusted through. ICK!