What's the oldest Chimay you've had?
Chimay can go a LOOOONG way. I had an 81 & 82 Chimay Blue in 2003 (clearing my cellar to move.) The 81 was stunning and the 82 had gone very downhill. I had a 500th anniversary Grand Cru at the Kulminator in 2001 (brewed in 1986) and it came close to making me bocome a monk. All sherried (in a good way) and plums and chocolate.
I've had Thomas Hardy as old as 15 years and it holds up.
While people will probably ask where I live and want to come over, I have them that old because other than one friend who likes them, none of my buds like that kind of beer. We drank a couple of the 15's over the holidays and they had a very smooth quality almost like a good port.
I once had a 5 year old Chimay Grande Reserve and it was amazing. I can't even imagine what the 15 year old must be like.
Any beer with sufficiently high alcohol should age well. I read a story about some 10%-ish ales unearthed from the basement of an old brewery in England that were a little over 100 years old. Apparently the ale in them had held up quite nicely.