i started replying to every comment here, then lost most of my work, so here's the i'm-pissed-off-so-this-is-what-you-get retry:
stouts: only the big boys benefit from aging. a 5-year old Guinness is going to taste like ass. being barrel-aged isn't a prerequisite for aging.
lagers: drink fresh, they won't improve with age and you risk oxidation. part of making a lager is to age the beer, cold, for several weeks/months to clarify it. once that is achieved, there is little additional benefit to aging, vs. risk of oxidation (AKA ruining it).
sours: assuming the beer isn't pasteurized (Rodenbach, most Lindemann, most New Belgiums, etc.) they can be aged almost indefinitely. the bugs in the beer, particularly brett, will protect the beer. after several decades you might start encountering issues.
fruited sours: personally, i prefer them fresh. the taste of the fruit will change over time: it'll become more muted, more incorporated into the overall beer. some folks like this flavor, personally i like the fruit to pop out. YMMV.
Any of the beers these guys make these days loaded with lactose and whatever other fruit goop you don't want sitting warm on a shelf.
lactose: isn't fermentable by brewers yeast, so doesn't affect shelf stability - assuming the beer was made by someone who can keep contamination at bay. there are wild critters that can ferment lactose but that shouldn't be a concern with commercial beer. homebrew on the other hand can be iffy. much harder to be bug-free on the residential level.
fruit goop: for 99% of fruited beer, the goop is added during fermentation so all sugars are consumed. fruit doesn't affect shelf stability. HOWEVER, some yahoos like to add fruit at packaging - notably some milkshake IPA makers. these beers will (or certainly should) come with a warning: KEEP COLD AND DRINK ASAP. as long as the beer is in a fridge, the yeast should stay dormant and all is well. if you suspect that a can of warm beer has fresh fruit in it (again, a rare thing given how dangerous it is), just give it a light squeeze while ensuring that your face isn't in the way of the top/opening since that's where it will fail: if the can is rock-hard, back away quickly and call the bomb squad.
None of these pastry stouts get better with age
agreed. but they are more shelf-stable than the average beer, so no need to consume them like an IPA.
Why would anyone store anything other than barrell aged stouts and the like?
Honest question. Those are the only things I store.
My quad homebrew that i bottled maybe 10 months ago tastes much better now than when i bottled it. It was way too boozy to start but now tastes like i would hope it too. Again, like the aforementioned trippel, a high abv Belgian.
high-alcohol beer can be initially unpleasant (ever had a fresh Bigfoot?). long story short: there are several types of "alcohol", one of the types is called fusel alcohol. this is burn-your-throat rocket fuel stuff. fermenting a beer too warm produces them (hello homebrewers!), and making a big beer = producing a lot of alcohol = some of it will be fusels, in quantities you can taste. the good news is that fusels can, within a limit, "age out" - they chemically change to other alcohols that we find pleasant (or at least less offensive than fusels). hence, letting a big beer age will make it smoother.
coda: there is such thing as letting a beer age too long, even a 15% barrel-aged imperial stout. when i left DC i had a cellar-emptying party. some great stuff was had that night, but about a quarter of the bottles were over-aged: oxidation had done more damage than aging had improved the beer. a few beers that i had been looking forward to tasting for years were disappointments. since then i've limited my cellar-stocking and try not to keep anything for more than 3 years (except for sours and meads).
