It depends. Most are 14 days or there abouts, but it's mostly a wet age. Some meat departments are better than others, so it varies. The last prime rib dry age that was done at my house was 28 days. It was a true prime, not choice. Some of the stuff you can get a costco for will last a hundred days or so with out having to be frozen, not sure if it can dry age that long though. Wagyu A5 or grade 14 isn't cheep stuff though, $2300 for a ribeye roll.
Generally, the better the meat the longer it keeps.