I'm still growing too. When I was 10 the doctor said it top out at 5'10". Now his special charts say 6'6". That's why I self diagnose and avoid the doctors.
I'm wit ya there iex my mom forces me to go I might hav torn my meniscus slightly but I don't wanna go to the doc
You will not gonna muscle from running, you will gain leg muscle though. Most beef cake body builders can't run a mile, or if they can it'll be at an extreme slow pace. If you're looking to lose weight, run and eat healthy. If you're trying to tone up a certain muscle, you can do calisthenics (situps, pullups, pushups, dips, flutter kicks, squats etc). Health and fitness is huge, get in the routine early on - you'll be doing it for life