Seems unlikely to me, at 19 with legend potential.
Potential does nothing for training speed, unless the player has hit his skill cap.
5 weeks is not unheard of for outside d, if you are doing 2 or 3 position training. A lot of things impact training speed. For example, if the rest of his guard skills are very low and outside d is already high, it would slow training down.
Also, did he get 48 minutes at a training slot for all of those weeks?
Run of the Mill Canadian Manager