The meat is less than 5 days from slaughter date by the time that it reaches the retail store. I always like to age my meat 28 days before they cut, wrap, and freeze it. Most small local packing houses do not like to see it hung more than 14 days as after that the carcass usually requires a little more trimming and they are afraid people will ***** about not getting enough meat back.
As long as you keep the meat under 40 degrees there is no problem keeping it in your refrigerator for up to 3 weeks after purchase date. I do this on vac sealed steaks a lot. I have also done it on briskets and was pleased with the results. I think that some competition cookers age their briskets also. Google wet aging.