Not to be overly blunt, but at age 14, this player is simply displaying a lack of strength in the hands, wrists, and forearms. This is common at age 14, as some kids are beginning to grow strong quickly, while others will have to wait for their bodies to develop.
Best advice, especially this time of the year, is to put down the bat for a couple of months and pick up the dumbbells, grippers, wrist rippers, and the like. 14 is a great age to learn how to develop one's body strength.