TMG Version 7 has some problems running on the latest versions of the Windows operating system. TMG Versions 8 and 9 were released to deal with many of these issues as well as fix bugs and add enhancements. For these reasons I suggest you try to purchase a license for the final Version 9 while you still can.
See the topic: http://www.whollygen...nstallers-v905/
If you do choose to contact Harry to purchase a Version 9 license, give him some time to reply as selling these is a part-time activity for him.
No matter what version of TMG you choose to use, TMG will only run under Windows. The only way to run TMG on a Mac is using some form of program which allows a Windows operating system to (also) run on that Mac. Glenn Gilbert (who unfortunately has since passed away) posted several instructions about doing that, especially using Parallels. His most current posts deal with running the final TMG Version 9 on a Mac, but they would probably be adaptable to Version 7.
Note that you will still need to obtain and install an appropriate Windows OS as part of this solution. If you choose to stay with your existing TMG Version 7 then I recommend getting Windows XP. Otherwise the TMG final Version 9 will run on the latest Windows 10.
Hope this helps,