Suggest Treatment To Improve My Posture

As a child, I slouched terribly. At about age 13 I became aware of the fact that my back was hunched and not pretty and flat like every other girls’. I improved my posture SIGNIFICANTLY, but at 15 I have seen very little difference. I also see many other people my age slouching with no hunch at all! My question is whether or not it’s too late for me to fix this and have a straight, flat back because the slouching occurred during my growth stages. If I can straighten it out, please tell me how to do so because I am not seeing much result by improving my posture. This is something that really affects my self-esteem. I have included photos of both my own back and a straight back.