I regularly use 5-7 year old oil (hoard when they are almost free after rebate, now the best I can get is about $2 / qt synthetic).
From my observation the plastic bottle gets "soften" and colored more "yellow", I suspect some oil components get into the plastic and soften it over time. There are also some additives fall out of suspension and settle at the bottom. It is probably fine to use, just not as good as fresh or the newer formula out there with newer spec. Most oil have way more safety margin than we need anyways. My storage condition is in a garage that's almost 50-70 year round, on a shelf, humidity is low, out of sunlight.