Hello,
I would like to know your thoughts on girls 13 years old using. 29.5 balls for dribbling and shooting in the off season. Also, what's your thoughts on weight training.

At 13, kids should use the size ball they will be playing with.

Weight training is a tricky issue. I certainly would not start them on it until they are well into puberty. This question is probably better asked of an exercise physiologist or other weight training specialist. Try the PE department at a local college. The problem with asking a basketball coach this question is you might get an answer.