The shelf life of gasoline is around 6 months before it starts going bad and turning to varnish.
However if you don't properly store the gasoline out of the sunlight when you have the gasoline in gas cans the heat of summer can cause the gas to evaporate.
So the gasoline can evaporate from a gas can before it goes bad.
It's best to keep the gasoline in gas cans in a shed away from your house that contains no flammable ignition sources.
In your car it's best to use the gasoline well before a few months so that it doesn't go bad.
So drive your car at least a few times per week to use some of that gasoline or don't fill your gas tank to full if you don't drive your car often.
Gas can go bad and then clog your fuel pump, fuel lines, fuel filter and even your fuel injectors.
Adding some fuel stablizer to your gasoline can also help extend the shelf life of your gasoline as well.