I have had my 250 ml bottles for about three years, I see no reason why it should age so I am not worried about it. Keep the bottles tightly capped. I also put the two bottles in a large zip lock bag with the syringe, spare filler plug screw, little hose, etc. also in that same zip lock bag. If I was concerned that oxygen or perhaps any organic compounds could get in or out of the bottles, I am sure putting them in a zip lock bag helps too.
I do not recall ever noticing any oder from opening either oil bottle, which implies that there are not any volatile compounds that would quickly evaporate. If there was any odor, it was so weak that I did not notice it.
I always re-use my drain plug screw, but I put a new layer of Loctite on the screw each time.
I store the oil bottles in a dry place.