I wouldnt show him any anime besides Naruto, One Piece, Pokemon or Digimon. To watch Aot, I would recommend to be atleast 14 years old, because thats the age where you learn to differ fiction from reality. Even if he doesnt care about the gore and is very smart, dont let him watch shows which are rated R+, because that triggers something inside his brain. I cant exactly tell you what it triggers, because Im not a psychologist. I have also seen some things at a young age which Id rather avoided. Please, dont show shows for adults to a ten year old. (Im sorry for my bad english, Im from Germany)