The oldest version I can support in the latest version is macOS 10.12. The previous version, Tiled 1.8.6, could in theory still be compiled on macOS 10.10 against Qt 5.6, but I don’t currently have such a build available. I’m not sure what is the last available build that worked on 10.10, but you can get older versions from https://github.com/mapeditor/tiled/releases