I have had 4 and 5 year old Belgian ales, and they developed some nice character.

There's a fantastic bar in Antwerp called Kulminator that specializes in aging Belgian beers. I was there one afternoon back around 2007 or so for somewhat of an extended session, and I recall trying older and older beers until finally I ordered a Kriek from 1976 (I remember this as it was the year my sister was born). I never got round to trying a beer that was older than me though...

Not in my house. :D

I had the misfortune to taste Billy Beer fresh. My father bought a sixpack when it first came out. He drank one. I drank one. My alcoholic brother-in-law drank the remaining 4 a good five years later. It was as bad as any cheap beer I drank in college. Nothing short of complete dehydration could improve it.

you can age guezes and barleywines 10 to 20 years, really.

conditioned bottles can keep longer than regular bottles.

If the beer is getting a lot of it's flavor and aroma profile from hops - 3 months max is the shelf life if not refrigerated. If you have big hops beers like India Pale Ales and Double India Pale Ales (like Pliny the Elder, Alpine Expo, Double Trouble, Hopslam, etc), they should be consumed soon after bottling as the hops fade fast.

I've had some domestic beers that were 9-12 months old and they were pretty bad... Can't even imagine how disgusting 35 yr old beer would be