We have a closet located in the central part of our house, far away from outside walls that is our desiganted aging closet. We spend most of are time in the upstairs part of our home, so we keep the downstairs part at 68 degrees.
It has worked well over the years for beer aging. Currently aging a Belgian Tripple which seems to be best when aged at least 6 months.
Parents have a big concrete garage closet that is 1/2 way underground which works great for storing/aging beer. Stays pretty constant temp year round ~55-65. I always call it my "beer cellar", currently has a few bottles of commercial brews and roughly 25 gallons of homebrew fermenting/aging in it.
When we built our house (which is on a pretty steep grade), I had the chance to design the basement. The room in the back that is completely underground is my beer cellar/fermentation room. I try to keep it as close to 60-65 deg F as possible. In it I have several Gorilla shelves full of my barleywine/Belgian/Imperial collection. There is also a fridge for chilling IPAs that aren't getting long-term storage. The next upgrade is to bring in a separate cooling/humidity control unit to keep it at peak condition.
I do my best, given the temps in FL, to keep only beers I know that will age decently well stored in a close in the coldest room. It sucks cause the temp is usually around 72 - 74 which is higher than normal but with that said I do intend to consume most of my beers over the next 2 -3 years or until I get find a solution to keep 30 - 40 bottles at around 55 - 60 degree sooon.