I'm not a butcher, but what I understand is that "wet aging" is the euphemism they've come up with for the product of huge meat processing plants, where they have the meat wrapped up in these individual vacuum-packed plastic bags - now I'm seeing not only the big pieces of meat like 20 lb pork loins and similar sized hunks of beef strip loins/rib eye, but smaller cuts as well, coming from the factory.

"Dry aging" is what they do with meat in the cooler before its cut up - that can vary from a few days to weeks. And I understand that this is how the fancy steak houses do it - they buy the large cuts of meat that you refer to, then wrap it in cheese cloth or something similar that 'breathes' but protects the meat from drying out too much, changing that wrapping every few days in a cold store, and the end result is a steak they can sell for $70 a plate.

But leaving a piece of meat in a sealed bag for an additional 3 weeks after you buy it? I don't think I'd try that. I'd guess that the "best before" date stamped on those big sealed packages is there for a good reason.

It's been my experience that meat from the store is already close to going bad. Just a couple more days in the fridge and it's off. Plus, when it's sealed, it gets slimy and smelly.
I would never do this with store-bought meat. I do buy meat from a wholesaler through a coop for my dogs. This stuff is much fresher as it hasn't been sitting out on the racks, freezing and thawing day after day, getting cut and wrapped in small packages. Perhaps if you bought full sized roasts from a real butcher you could try it. I have cut meat off a large pork shoulder for a week and it still smells fresh, but I don't seal it up, just cover it lightly to keep it from drying out. This meat is much fresher than store-bought, though.
I know with my home grown chickens it's amazing how long I can leave it in the fridge and still doesn't stink like store bought. I often take a week or more to use a whole monster Cornish-x up, it makes as many as four to six meals for my husband and I, plus 7 quarts of stock and a meal or two for my 3 dogs.