Is it true that he can request a change of parent at that age?

No, it is not true that a child can pick where her or she wants to live when they become 12. There is no law or case that says that. It is an urban legend. As they get older they may have more input, but there is no magic age where what a child wants means that the child will get it. Even 17 year old sometimes can not call the shot. IT depends on their maturity among other factors.