Fuel does break down in as little as 3-6 months depending on the blend. You'll notice older fuel doesn't evaporate and "mist" so well as fresh fuel. I wouldn't sweat anything under a year old though. Mix if 50/50 with fresh just to rule out any chance of hard starting.
I ran my Galaxie for a brief time on 3 year old gas after getting it going after it sat in the garage for a few years. The fuel didn't atomize well but witha little squirt of fresh gas in the carb it fired up and ran fine on the old fuel. Another time I had 20 gallons of gas from 1991 to get rid of. I just mixed a few gallons in each fillup in my truck and noticed no difference, though playing with it on the ground it would take a few seconds of holding a lighter to it before it would flash. I had no way to get rid of that quantity without paying for disposal, so no problem dilluting and burning in the truck.
Anyhow, for less than a year old, just mix it up with freshh and don't sweat it. I doubt if you'd have any trouble running it straight but mix to be sure.