The oldest home brew I have is an imperial stout that is over 18 months old and it keeps getting better and better.
I have a Brew Dog beer that has a best before 2023 date, so they are expecting it to be good for ~10 years.
I just did a 2004, 2008 and 2012 Sierra Nevada Bigfoot vertical tasting. Actually the 2004 wasn't that great, but it actually was a screw cap so people were saying that might be the problem. But the 2008 was very good.
So the message is, beers can last a very long time in the bottle and still taste very good.