Definitely to small to sex imo. Nuchal humps and fins mean nothing in sexing rd/midas cichlids. The only way to tell would to wait till he got some size on him and show us some pictures of it's vent.
View attachment 383956try to see underneath him... or take a pic of under him.. this is the vent and how it should look if male or female... very sweet fish..but cannot tell unless you vent..