Player growth is individual and doesn't depend that much on rating.
Last season my first squad gk (20years old then) became scout after first few trainings. By the end of season his rating increased from 64.x (near 65) to 68 (45+ cones). He was best player and still is in top of my squad, but some weaker (5 stars) and younger players didn't progressed that much or they had similar growth difference.