Fuel goes stale because, all the highly volatile particles have all evaporated leaving you with fuel that does not burn well at all, think of it like on a hot day and you open your fuel can and you can see the fumes coming out and smell them. Also with two strokes over time the petrol breaks down the lubricating oil and leaves you with a pretty ugly mixture that does not burn cleanly and may well not lubricate your machine properly.
As for your mower, I would be fairly sure that it would be a powertorque engine, but I am not sure what got exported, Bruce would have a better idea than me. Try putting a tiny bit of fresh fuel down the spark plug hole, if it will not fire then, we can go into more detail.
