In my experience, a guard with medium height will take a bit longer to train in guard skills than a shorter guard. I recommend playing him at point guard. To start off, I would train his Outside Defense and Passing to strong. After that, I would give him 1v1 Guards (if you want to train his Handling and Driving) or 1v1 Forwards (basically the same as 1v1 Guards, but it trains IS more).
Training 1v1 Guards will also train his Jump Shot a little bit. If you really want to train his JS and 1v1, then you should probably wait until it is a 2 game week (Allstar Break, playoffs) or he doesn't get enough minutes at the point guard spot.