Wanting robux and things like that are probably unavoidable due to peer pressure and exposure to videos and game-mechanics telling them they want this. It’s probably been like this forever, you always needed the same merchandise your friends had.
I’m curious: Do you know what he (at his age) thinks about your perspective on things?
Does he have other hobbies and still wants some immaterial in-game items / currency? Does a kid at that age grasp the value / alternatives? I suppose this all depends on how much time someone spends in a virtual world. Sure you need/want some goods there if this is a major part of your life.