It’s not the best game, but considering he was a teen when he made this, still an impressive feat.

Later on he made the Build engine after seeing Doom and saying to himself: “I can make that”. This was notable enough that John Carmack, inhuman programmer of id software, gave him a call to ask how he achieved looking up and down in the build engine.

https://www.mobygames.com/game/388/kens-labyrinth/