I have about a half gallon of 20% that is about 8 years old (haven't driven in about 5 yrs). It smells ok, but I was wondering if it would hurt to run it?
It won't really hurt, but it might be a bear to start and tune.
Always start with fresh fuel till it's tuned right, then you can try the old one. If it doesn't want to run the same, it's a good weed killer.