In my experience, dark, high ABV beers age very well.
I brew a 10% Russian Imperial Stout every year around this time and age it 6 months to have in the fall. I've saved several bottles for more than a year and do a vertical tasting with each new batch. Each year, the aged version of the same beer is much, much better than the fresh batch. It's not even close.
When I had a couple bottles from 4 years / batches saved up we did a tasting of all 4 (aged 3 years, 2, 1, and a fresh bottle.) The difference was remarkable between fresh and 1 year, subtle but noticeable between 1 and 2 year bottles, and undetectable between 2 and 3 years aging. So the is a ceiling to it.
Another example: I brew an 11% Belgian Quad every now and then. I gave a few to my brother along with some pilsners I made. He gave one of each to a friend of his at a cookout. The guy is a bud light type, so he just had them in the back of his basement fridge until my brother found them 4 years later. He gave them back to me and we cracked them open. The Quad was so spectacular I called my neighbor to come over to try some. The pilsner was completely bad... horrific. Skunked and disgusting.