You can throw maximally from any distance; long toss only has one advantage, its fun!
Long toss teaches your body to release at an incorrect angle and if you are using the traditional pitching mechanics they are nothing like what is happening in long toss.
I have all my pitchers do all their maximal throws from the mound that is much better
to train closer to what is actually happening mechanically.
Is your son biologically 12 also? Or is he biologically 11? This needs to be known.
If he is under biologically 13 years old you should not be throwing competitively or training ballistic ally more than 3 months a year! Only adults need to maintain year round
maximal fitness.
quote:“a lot of stretching to increase flexibility”
Laxity from stretching is a negative not a positive! A loose shoulder capsule is to be avoided, not produced from stretching, it has been established by the Center for disease Control that stretching is bad for you and especially the over exaggerated baseball stretches. If you stretch before competition you loose 6% of your ability to perform. Drop the stretching.
http://www.drmikemarshall.com/...sMuscleInjuries.html