Attempt to install Qt on OS X gives 'You need to install Xcode 5.0.0', but this version is so old it's not available
I ran into the same problem and solved it by following the instructions here. This link describes a similar, but slightly different installer issue.
To summarize, you need to ensure that the Xcode command line tools are installed and set up correctly. I already had them installed, but had to go into Preferences -> Locations in Xcode and set the dropdown to the currently installed version.
The link shows an earlier version of Xcode where the path is actually Preferences -> Downloads -> Components.
Once I'd made this change, the installer continued successfully.
The solution that worked for me (on OSX Sierra XCode 8.2.1) is to open XCode Preferences -> Locations.
There is a drop-down menu named Command Line Tools. Select the available XCode version here. Then restart the Qt Creator installation.
taken from the link above, this resolved my issue:
sudo /usr/bin/xcode-select -switch /Applications/Xcode.app/Contents/Developer