That’s incredible. Your son has far, far, more patience than I ever did. I still haven’t managed to clock most of the games I grew up with, such as Dangerous Dave, Prince of Persia 1 & 2, Wolf3D, Doom 1 & 2, Crystal Caves, Aladdin, Lion King, Jazz Jackrabbit, Mario (NES), Pokemon Red (GBA), Crash Bandicoot (PS1)…
Every now and then I try to clock one of those old games, but then I get stuck and/or lose interest, and move on to something else. Even among recent games, I spent over 400 hours playing BotW and only managed to do two of the divine beasts. I also have over 200 hours in TotK and still haven’t gotten to the first major spirit quest. Similarly, got several hundreds of hours in Morrowind, Oblivion and Skyrim, but never actually completed any of those games.
I think the only game that I recall beating would be the Bio Menace trilogy - which I finally managed to complete as an adult, and that too thanks to DOSBox’s save states. Oh, and Diablo II too, it someone had the perfect mix of action + story + game length, to keep me interested till the end.
Honestly I’ve no idea how people manage to stick to one thing for so long and see it thru till the end, without losing interest or getting distracted by something else.