How to tell how long beer will age?

I'm curious to know how some breweries know how long their beer will age.

Local brewery here in MN, brewed a barleywine called Commander for the first time, and they claim it will age until 2020.

How do they know that? Is it more of a guess based on the style?

Sorry for not searching, but I'm using the mobile app and the search functionality isn't great.

I don't think they know specifically but i think they have an idea how long the bottles will continue to gain comlpexity with time. They won't really go bad after a certain amount of time but won't gain much more in terms of flavor after a while. I had an 8 year old barleywine a few months ago and don't think that it would have tasted much different from a 20 year old bottle. The short explanation is that they kind of peak

Cellaring and Aging Beer - Imbibe Magazine

I think it's more of a guess with style and expectation at this time, based on some people who have managed to age some styles. It's not been something that has been widely done, though is becoming more common.

My brother just opened a 5 year old Trader Joe's ale on Thanksgiving, I'm PO'd that he didn't taste it, but instead let the others try it. (I'm allergic so I'm void). New Beer: Trader Joe's 2011 Vintage Ale | Serious Eats: Drinks You'll see that others have done the same and commented.

In part, some has to do with the higher alcohol levels and possibly lower hop styles. But at this point, who really knows for sure. I apparently have some simple Leinenkugels from a variety case and a few stouts from back when I wasn't allergic 9 or so years ago, and I've been told they still drink well. (I was going to dump them just for the bottles, glad it was tasted by someone willing. Instead I left them in the cellar.)