Some plastics are OK for storing alcohol but some may leach out chemicals and indeed, allow O2 to pass through the walls.. Not sure that I would age anything for several months in a plastic container that was not designed for storing alcohol (say a container designed for storing water, or juice). Better Bottle (TM) uses PET and their containers are said to be very stable and are said to be suitable for fermenting and aging... I do use BB
In addition to my glass carboys I use plastic but have never bulk aged much past 3 months in either type. I use both Better Bottle and Bubbler plastic carboys and like them both.