I found this answer from the Godot QA. It looks like MacOS 10.10 (OSX Yosemite) or newer is required. From everything I could find online, the oldest version of MacOS running Godot is version 10.10.
I've used Godot 3.0 with a older Mac laptop that was pretty old, at least 4+ years, and it ran Godot fine. This list of Mac computers that use OpenGL from Apple shows that most every Mac from 2011+ should, in theory, be able to run OpenGL 3.3.
I think that so long as the Mac is using a recent-ish version of MacOS and was made in sometime after 2011, it should probably be able to run Godot. I wouldn't quote me on that, but that is what I would guess.
Hopefully this helps!