Have to disagree a little bit. IPA's are definitely best when fresh before the hops drop off. Inside 6 weeks for IPA's for the best enjoyment of how the beer was meant to be drank.
BUT Belgian quads ,barleywines, imperial stouts, high abv IPA's such as 120 minute by Dogfishhead at 18 %, all age wonderfully. It can be debated better or not that depends. What you get is less alcohol burn as I'll call it in these higher abv beers. I have some beers in my cellar that will go 1,2,5 and even 20 years . A lot even have "ages well" , " cellar for a later date " etc on the bottle.