[bandwagonfan]

Players template plays the biggest part but there is also a random factor how his skill points are distributed (Player/Edit on the left side you can see player template)

Sometimes before age ~22 i believe player template can change from offensive to two-way and then their potential for offense/defense also changes.

I dont pay as much attention to training anymore since if you give a player enough ice time and have him selected in training screen they will grow close to their max potential anyway. In rare cases they just wont grow at all doesnt matter what you do.

Training definitely needs much more attention from developers as it seems too random atm. I have played around a bit with development options for player peak age/physical peak age and havent noticed any significant difference