Sour or not?
If a beer is aged in a barrel, does that make it a sour? While lots of sour and tart beers are indeed oak aged, the process of aging a beer in a barrel does not necessarily lead the beer to become sour. Sour or tart-tasting beers are usually made by introducing wild yeast or bacteria into the beer, so if no wild yeast or bacteria is allowed contact with the beer, the resulting product shouldn't taste sour, but will instead have lots of rich flavor from the oak barrel.
What kind of beer?
Beers of all types can be barrel-aged, but there are some styles that hold up to it better than others. Most commonly, you will find darker, higher alcohol beers aged in barrels because:
A) The strong base flavor will stand up to the intense barrel character that comes from using a whiskey or wine barrel, and
B) The alcohol helps to preserve the beer so it won't have stale flavors from extended aging periods.
Russian Imperial Stouts, Porters, Scottish Wee Heavies and Belgian Quads are all strong beers that are typically aged in barrels. Some lighter styles like Belgian Farmhouse-style saisons can also be aged in barrels, but the desired flavors are usually not derived from the barrel itself. Instead, they come from the addition of wild yeast to create complex tart and sour flavors.
What kind of barrel?
When it comes to buying barrels, most brewmasters prefer to shop in the used section of Barrels R' Us. Much of the character and aromatic quality that make barrel-aged beers so unique actually come from the liquid that was in the barrel before. While it is not unheard of for a brewer to use a fresh oak barrel, most commonly a used whiskey or wine barrel is preferable. Some breweries are even using rum, tequila and brandy barrels to age their beers!
Should I age the bottle?
Lots of craft beer enthusiasts are building home cellars', or places where they store bottles that will age well. A home cellar can be as simple as a kitchen cabinet or as complex as a temperature and humidity-controlled room in a basement, depending on how far down the rabbit hole you want to go.
Personally, I usually hold on to a few special beers that I would like to have around should a special occasion arise, but don't tend to hoard large quantities of beer. The way I see it, if the brewery went through all the trouble of aging a beer for 6 months or more, it is probably tasting just how they want it when they release it, so I don't feel compelled to age the beer at home before drinking.