My first one to switch did so recently. Gave him an open offer to help get going if he ever got interested, then proceeded to just go about using my linux system for our multiplayer gaming and couch gaming hangouts.
It took a little less than three years from when I first switched for him to follow.
My sister is also on linux, has been since she took my gaming laptop as her own, and she never felt a need to switch it back to windows.