I hang mine for 17-19 days. About 90% of tenderization that will occur happens in the first 12 days. After that, its all about flavor. As the carcass loses moisture, the beef flavor is concentrated. A good layer of fat is needed for proper dry aging. The fat helps the carcass retain moisture during the aging process and also serves as a protective barrier to the mold that will start growing. My butcher trims the moldy crust off with a draw knife, then rinses the carcass off. Some extra trimming is done after making the primal cuts. Hanging is really just controlled rotting. One thing to remember is that dry aged beef will not last as long in the freezer as wet aged, and the longer you age it the shorter it will last.
.......and If your dry aged beef is dry, you either overcooked it, or your butcher doesn't know what he's doing. :nod: