The fuel age issue is something about which I've considered starting a separate thread.
Since I don't get to fly much these days, I've got a lot of experience with 'old' mogas. Since there are so many variables, I'll try to document all my specific conditions.
Carb'd 160 HP RV-4. I run *premium* *no-ethanol* mogas (E-free because of the very old E-vulnerable fuel pump, and very old tank sealant.) It's not unusual for the plane to go well beyond a month between starts.
For several years, I've had problems starting the plane after it's been sitting. I spent a lot of time blaming the mags & carb (I did find a couple of carb issues, which didn't help the hard starting issues). Frequently, I'd end up either running the battery down or flooding the engine. Then, the next day, I'd go to the plane and it would start right up. Finally, a light went on in my head. The next time I wanted to fly after a long hiatus, I went to the plane early, ran the boost pump to fill the float bowl, and then, with mags off & mixture at cutoff, I'd pump the throttle repeatedly to empty the bowl using the [edit] accelerator pump. After a long enough interval for all the puddled fuel to evaporate (overnight, the 1st time I did this), I went through a normal boost pump/prime/crank procedure. Fired right up. And it's worked every time, since. If the plane's been sitting for more than a couple of weeks, I 'purge' the float bowl like this an hour or so before the planned flight, and it always starts quickly now.
Now, to causes. We all have heard about the perceived issues with 'old' mogas, vs avgas. I'm not qualified to render a verdict, but my belief is that mogas (E, or not) has more and different 'volatile' chemicals that help it light off, than avgas. And my belief is that those chemicals, when in a small volume, high surface area place like a carb float bowl, can evaporate fairly quickly. The fuel in the tank seems much less affected; pumping the bowl dry and refilling with fuel from the tank solves the problem; at least for me.
As possible reinforcement to the theory, I've seen very similar, but worse, symptoms with my 2stroke lawn power tools. With those, not only are the volatiles gone, but the oil % goes up, too.
Note that I keep fuel in sealed 5gal gas cans, and I don't have issues with the fuel, even after months of storage.
Above is just offered as additional data points, and *my* theory of why the 'old gas' legend exists. I'm not an authority, and I didn't sleep in any hotel chain last night.
Charlie