You are going to hear a pretty wide range of opinions to your query, mlj. They certainly do get old and you can delay the "aging process". Personally, I keep any nic liquid, PG, and VG in the freezer in their original containers until use, unless I happen to decide to transfer them to glass bottles first. I also keep VG and PG in the fridge. I have used some nic liquid that is ~3 yrs old with no apparent degradation, but that is just my experience. Flavors I keep in a cool, dark place. I have refrigerated some with no deleterious effects, but many will point out the humidity in the fridge and problems from it. But the containers are closed, so I don't really know what to think.
Bottom line, cooling is cool for your goods far as I'm concerned. I'm sure there will be other experts who will chime in to tell you more jewels of wisdom as well. This is just my
Good luck with DIY -- it's a lot of fun as long as you don't get overly entangled in the minutia of measuring, additives, etc. Just keep an open mind and have a good time with it while being careful and respecting the nic liquid.