Aging Beer

Do you have luck in aging beer?

I have a dedicated beer fridge in my garage. I have beers for immediate consumption, and beers that i age. What i have been finding, recently, is that any beer aged for up to a year or more, just tastes bad.

For example, I opened a Grand Reserve 2012 2 weekends ago. It lost the great flavor i remembered when i first bought it. It's like all of the flavors and nuances of beer start out like the night sky. Open and greatly varying. But after a year, it's like all of the flavors get sucked up into a black hole. What i'm left with, is an overly malty, muddled beer with no distinct flavor.
This happens with nearly all of my aged beers. Bourbon County brand stout, was aged a year, and i had that same nasty ball of malt taste, so i have yet to experience a good one of these.
Mikkeller is a common offender of these, seeing as most of their beers sit on the shelf for a long time.

I still have a pumpkinator from 2012, 2 from 2013, and 1 Grand Reserve's from 2013. There are also a Bayou Teche Loupe Garou from last year, Stone Vertical Epic 12 and 13, 2012 Bayou Teche Joie Vive, and a couple others.
I'm just now getting into sours, and this seems like truly, the only style that can benefit from aging.

What is your strategy when if comes to aging beer? From now on, i'm limiting shelf life to 6 months, max.