This is his first official update, he's been around since just after the last one, which was about a month ago. That's how long he's been working on AI War. He's been professionally programming C# for a couple of years, and otherwise before that. I'll let him tell you his resume if he's interested in doing so. But suffice it to say, he's an experienced programmer, in C# and otherwise, in a professional (business) environment as well as prior hobbyist game programming stuff (and some work for some other indie projects).
Getting used to someone else's architecture, though, is a whole other ball of wax, and hence his comment about being new. Generally when I train new programmers (and I've trained half a dozen) on a complex system, it takes a few months for them to really get acclimated. Keith's been such an awesome fit that he was pretty much to that point in a matter of weeks, because he's been an AI War player and forum member since last June, and so was deeply familiar with the game itself, as well as just happening to have almost the perfect background in programming/C#/game development for this specific position. But even under such optimum circumstances, there's a learning curve (he's basically having to climb inside my head and think like me, when it comes to architecture and such, right?).