Depends on his potential. If he's Perennial Allstar or worse, definately train JR until 9. If he's Superstar or better, you could eave it and try to cap him.
As to when to train it, you can wait with it if you want him to get better quickly. Train OD first so he won't be a liability on defense while the rest of your team carries the offensive load. Then when OD is 12 train Passing until around 10-12 (depending on potential) so he'll know when to pass if he can't get a good shot. Then you can train JR until 9 and you'll have a nice player!