His appointment at the age of three is officially recorded in the Registers, and in Callahan's volume, LIST OF OFFICERS OF THE U.S. NAVY. As well, the situation of his appointment at that age is recorded as being unique, and not occuring at any other stage, in the United States Navy, so I believe that it is the only one of it's kind in the United States, and probably the world.
Also found another revelation, this time on Confederate Navy officer, Beverley Kennon, which, if true, is very, very unsual. See my entry under a separate posting.