Plug probably a good place to start based on what you said there. Also check your choke. Take the lid off the air box (if it has one) & check the lever is actually moving the chokle plate. If no visible choke plate you probabyl have one of the older carbs where the choke was an enrichening valve (i.e threw more fuel in). Post back if that's what you find, but try a new plug first. Nothing will happen if there's no spark!
1 month old fuel might cause something new & highly tuned to go in the huff, but to put it in perspective when I ran my Merc in after the rebuild, I used fuel that had been lying around for nearly 2 years, then added more oil to make it 25:1 & it started first go!
For the cost of a spark plug, give it a try. If you have a spark friend, ask him / her to megger both it & the new one (insulation test) - it's a good demo of how the insulation eventually breaks down.