Most of the major VR headset companies (Oculus, HTC, Sony) do not advise that children under 13 use VR. You have to be 13 to sign up for a Facebook account - although I'm not sure if you meant "not allowed" in the sense that you won't let him sign up for an account.

A game's age rating only covers the suitability of the content in the game in terms of things like violence, strong language etc. It does not imply that the game is aimed at or would be enjoyed by a particular age range. There is no special consideration for VR in terms of age ratings.