My daughter is now 16 and she has played with head only since the beginning. She is skinny but strong, and ranked top 50 G16 national.
As I recall she jumped from the junior 27 length radical to the Radical MP around 13 years old. So from a weight standpoint is was from 10.3 to 11.3. now plays with the youtek IG Radical MP @11.3. I have been stringing her racquet with the same hybrid set up for years. 17G poly mains at 56 and 17G syn gut crosses @58.
She is one of the few girls that I see that doesn't play with an all poly set up. We tried it, but she doesn't like the lower tension.
no shoulder or elbow issues to date, (knock wood) and trains 7-9 hours per week.