My son is also 3 1/2. I've also wondered whether he has a eidetic memory, but I don't think he does. Nevertheless, his memory is very good. He began reading shortly after 2 and I think he's now reading at a grade 3/4 level. He reads by sight, it seems. Once he's learned a word, he never has to sound it out again. He's also very into world geography. Before he could read, he learned many countries by shape. Now that he can read, he knows them by shape and by identifying their names. However, I do not think he could do a puzzle like you describe above. That sounds very impressive.
Welcome to the forum! I've found it very helpful and reassuring to hear other people's stories.
