I'm sure you'll get a large number of ideas.
When S was that age: 3 days a week Hoefflins (1 hr exercise [a variation of aerobic which focuses on arm, shoulder, and core] with other pitchers, 2 days long toss (everyone has a different thought on LT) (until he began losing form), 3 days off the mound (could be a light day or heavy day depending on any number of factors; throwing up to 100 feet mixed in with 60 feet).
He didn't do bands and began lifting 5 days a week at school under supervision in 10th grade (not nearly as well supervised as College and Pro, but got to start somewhere).