To the best of my knowledge, engine oil inside the engine goes acidic with time, and there are additives in the engine oil to cancel this out. Synthetic engine oils have enough of these additives that can keep them ok for a year, non-synthetic oils have a lot less and are recommended to be changed every 3 months.

So, if the oil is on the shelf in your garage, it stays ok.

If it is in your car, and it is synthetic, change it at least once a year.
If it is in your car and is regular oil, change it at least every 3 months.

In colder climates, where people store their motorcycles for the winter, it is recommended practice to change the oil before storing the bike, and again immediately afterwards before riding it again in the summer.