Freshman year of high school my son was 5’11” 135. He had just spurts from 5’4” 120. His mother is a personal trainer. Until the growth sport she worked with him on stretching, pliability and strength training relative to his size. There’s no sense breaking weight lifting records when you haven’t grown. Plus there’s the issue of growth plates.
Once he grew and needed to put on the weight he ate quality food like crazy and drank whey protein shakes. There was a point when his head was in the fridge so often I thought we needed a glass door.