Buy them a copy of "Human Resource Machine" on Steam or (preferably since there's no DRM) Good Old Games. It's a gamified version of what writing machine language on the old 8 bit CPUs of yore was like. The puzzle challenge in HRM is authentic in the sense that it derives from the natural constraints of having a single accumulator and very simple instructions rather than unnaturally injected constraints like the Zachtronics games, which are good but I wouldn't recommend as a learning tool.