"Don't age any beer that started its life as a hop-forward style. No, your 120 Minute IPA is not better after four years. And don't age beers with coffee, unless you like your beer to taste like green peppers. Coffee flavors fade relatively quickly, and can evolve over time, often into something vegetal.
"Do age malt-forward English beers. Old ales, stock ales, and English barleywines can develop leathery and umami flavors that enhance the hard work that the brewer has done. Beers with wild yeast (brettanomyces), as they can evolve in fun ways over time: Stick a six-pack of your favorite funky beer in the closet, and drink one every year 'til you find the sweet spot." -- Nick Bondi, bar manager, Jerry's Lincoln Square/Andersonville/Wicker Park (Chicago, Illinois)