I'm 20, with 55 degree of postural kyphosis, i developed backmuscles by training hard in gym, as i try to prevent it, is it gonna get worse as i grow?

Scheuerman's Disease: This could worsen as the spine ages but your skeleton is about fully grown at your current age. Have you been braced or offered one? This can help with pain if you are experiencing any. I would focus on living your life and not on the what if's. Continue to strengthen your back extensor muscles, but be sure to maintain muscular balance as well. You should discuss this with a physical therapis.

May potentially get: Worse. But by focusing on trunk stabilization programs, and core strengthening programs, that will help you minimize symptoms, and ensure you are paying attention to proper body mechanics.