I use it Till it runs out. Probably 6 or 7 years old after opening. Never had any trouble with gas engines in the spring. I prefer to run them dry in the fall though as opposed to keeping any fuel in them. I use a plastic hose to drain them. Summer gas Goes in the snowblower can and the mix can for chainsaw. In the spring leftover winter gas goes in my Z turn mower which burns about 2 1/2 gallons per mowing. So that doesn’t last long.
Strike while the iron is hot. Live every day as if it were your last and one day you will be right.