Here's a video of someone beating Super Mario Bros., the original for the Nintendo Entertainment System, in under five minutes. The speedrunner finishes in 4:57.69 to be exact.
I'm sure there are some genuinely creative speedrunners out there discovering new ways of breaking Super Mario Bros. down into tiny, tiny pieces, but I can't imagine I could ever get "this kind of good" at a single game, though it's impressive to see the kind of memorization required to get through the game with pixel-perfect accuracy.
Have you ever played a game so much you could run through it blindfolded? I had a few Game Boy games that I completed over and over again, but I never bothered to record my time even if it felt satisfying to know I could sit down with the confidence that I would finish a game before dinner.