Well ALL fuel you run through the engine should be "good fuel".

Age alone does not make the fuel good or bad, as it tends to hold up pretty well.

Some guys here have run 10 year old fuel on their planes w/o problems.

Now that said, when you switch mixtures you may have to tweak the needles a bit, but usually not much.

-

If the fuel is cloudy, not the original color, etc. don't use it.