Quite definitely a male...
So I would suggest either stunted from poor water quality earlier in life, or very possibly simply a smaller growing fish...
In the wild, at best one or two of the absolute strongest fish born in a brood will survive. In the hobby the vast majority of a brood will survive and be sold. This results in a lack of natural culling of smaller/weaker fish which in turn promotes "less than ideal" specimen from surviving to adulthood... as well as breeding to pass on their less than ideal genes...
This is by no means a criticism of your fish. It's just an honest view of why he may not have the full potential of what nature intended. He still looks nice and most likely makes a great pet.