Aging beef is done two ways, wet and dry.
Dry aging mainly done for steaks, which are cooked VERY hot and fast, to around medium rare. What dry aging does is remove water, which intensifies the beef flavor. Even dry aging for one day with a coating of salt can cause a 16 ounce steak to lose a whole ounce of water. I do that all the time.
A long dry aging requires a big chunk of meat, because you will have to cut off the outer layer of dried meat. You can easily throw away 10 to 20 percent of the meat, depending how long you age the beef.
For low and slow smoking, I personally think you are better off with fresh beef. I have not done wet aging, so I can't say whether or not wet aging would work for low and slow, BBQ style cooking. I do not use aged beef for low and slow smoking.
Here are a couple shots of a ribeye that was prepared 24 hours before cooking with sea salt, and placed on a wire rack for 24 hours, then seasoned with black pepper, and grilled over very hot coals. It lost a whole ounce in weight in 24 hours -- all water weight.
I cooked it over VERY hot coals. It is charred on the outside, and hot but red inside. That is a very American thing. Some Asians would consider it burned on the outside. But, that char adds both texture and intense flavor.