A well made can will allow food to keep a century or more. The quality will decline with decades and decades but canned food is pretty sterile; it's pressure canned at temps up around 230 or more which kills virtually everything (pathogen-wise, that is). Modern processes include agitation which decreases the time needed to sterilize the contents. I expect that modern cans are probably more cheaply made, thinner and less durable than they were a few decades ago but I'd have no issues eating a 20 year can of food, provided it wasn't rusty or bulging.