Given that he started publishing games before he was 20 and had produced Commander Keen, Wolfenstein, and a couple of Dooms before he was 25, I'd guess he was w

Given that he started publishing games before he was 20 and had produced Commander Keen, Wolfenstein, and a couple of Dooms before he was 25, I'd guess he was well on his way in his teens. Not to say that success correlates with skills, I suppose, but he's fairly well-regarded as an innovator from an early age. Odd choice of example from the article's author.