Not sure we constantly try to sell our Enterprise product. You could look at it less cynically as we sell an Enterprise product to allow us to provide the Anaconda Distribution for free.
There's no "native" Windows support (yet), but I think it might work with some of the UNIX emulations (cygwin, mingw, wsl, etc.)
Not sure what the oldest working Linux version would be. However, NixOS has been around since 2003, so maybe quite old.
It runs fine on macOS. It works on WSL if you disable SQLite's write-ahead log (`echo "use-sqlite-wal = false" > /etc/nix/nix.conf` before installing), but it's much slower than running it on native Linux.
> What's the oldest Linux distro upon which it will run?
It brings its own libraries, so the primary question would be what kernel you use. I haven't verified any specific version, but you'll probably be fine. You might need to disable sandboxing though, since that makes pretty elaborate use of the various namespace systems.