I’m not an Elon Musk fan but it was 1981 when he was 10. There were far fewer resources for learning to program and make games in 1981 than there are today. Not to take away from what your nephew did, but there are currently hundreds of “how to make a game” tutorials available online in a variety of instantly consumable formats. There are even entire development environments focused on simplifying game development with low code workflows. In 1981 there wasn't even the concept of a widely accessible public Internet.