I think even with Stabil, I would not run the gas after few months old, the important thing is it would not gum up the carb with Stabil. I have a trimmer that I have gas with Stabil in for about 15 months. I dumped out the old gas, put in new one and started right up. Without the Stabil, I am pretty sure it would be a goner.
Also it depend how old the gas when you first bought it. Just because it came out from the pump today don't mean it is today's fresh. Also it make a big difference if your tank is almost full or almost empty. If the tank is full, it will last longer than gas in tank that is almost empty.