Here is my story - I am 5’9”, wife is 5’11”. Both of my sons were late bloomers but ended up 6’1”. I remember when my older first tried out for club volleyball when he was 12. He was barely 4’6”. There were kids close to 6’ with facial hair, he was the runt. The coach said it is so hard to tell at that age, some grow early, some late. We have video where sons were so very small relative to others on the court with them, but both caught up to the early developers. One ended up playing D3 volleyball, the other played club volleyball for SU. Never would have imagined it at their younger ages. You never know - some stay ahead of the curve and others catch up. So teach your grandkid all aspects of the game, he might end up a center or a point guard.