To bring and old MacBookPro up to date you can use MacPorts. First you should download and install MacPorts package from macports.org. There is a pkg file to use specifically for Mountain Lion. That’s the easy one. A little harder would be to grab working XCode with command line tools. You need to have Apple ID, not quite sure if there is different one to access developer.apple.com but mine works just fine.
Go and download XCode 5.1.1 and command line tools, file names are as follows:
MacPorts-2.7.2-10.8-MountainLion.dmg Xcode_5.1.1.dmg Command_Line_Tools_OS_X_Mountain_Lion_for_Xcode__April_2014.dmg
XCode requires accepting licence with the following command:
As you will install command line tools manually, then there is no need to go to XCode’s preferences – Downloads section. Still it would not probably work as Apple ID now requires 2FA which is not present in such and old operating system.
MacPorts itself require update:
sudo /opt/local/bin/port selfupdate
After that you can install various packages. Without updating you are going to have troubles installing things as there will be missing package dependencies. For instance, to install wget type:
sudo /opt/local/bin/port install wget