We don't support old versions because we don't want to support every version ever made forever, we don't have the resources or the will to keep switching back and forth.
Note that if we support any arbitrary old version, the people who like a DIFFERENT arbitrary version will argue why we don't support THEIR favorite arbitrary version.
What do you mean the command to download Forge for Mac's terminal? Just download the installer from https://files.minecraftforge.net/, make sure you have Java installed, and run the installer.