macOS Mojave was released last night. As is often the case with major macOS updates, Mojave dropped support for a slew of older platforms. But just because Apple doesn’t support installing Mojave on older computers doesn’t mean that it can’t be installed. dosdude1 has a utility that allows you to install Mojave on a lot of officially unsupported Macs.
I’ve used his patch utility to get High Sierra on my unsupported 2010 MacBook Pro and haven’t had an issues. I attempted to upgrade my 2010 Mac Mini to Mojave last night but discovered that the utility currently has a problem decrypting encrypted APFS containers. dosdude1 is aware of this problem and will hopefully be able to figure out what is going on so it can be fixed. However, if your older Mac isn’t utilizing APFS or FileVault 2 (which it really should be utilizing), you should be good to go.