From a visual point of view, using VR a bit is probably ok at his age, but definitely heavily limit the play time and plenty of regular breaks - for example I would not let my own child use it for more than 10hrs a week, and not than 30min without break. If he were to use it a lot at his age, while his eyes are still developing, then they won't develop in the best way, and he's more likely to need glasses for the rest of his life as a result. Growing eyes need to spend a good amount of time being able to focus at a range of distances and especially long distances (as we naturally do s lot of close work these days) to develop in the most ideal way, that's why one recommendation to try to avoid (or limit the extent of) shortsightedness, is for children to spend more time outside.