I don’t know anyone who thinks Aperture is the best raw converter, it’s easily surpassed in that category by several other converters. What it is, in my opinion, is the best combination converter/editor/cataloger/printer. FWIW.
With that out of the way, how are you trying to install it? It’s not even visible on the App Store at this point, unless you’ve already purchased it and had it installed. And if you’re trying to install from a disc, there aren’t any versions that were released on disc that would run on anything later than 10.7 or maybe 10.8.