
Just to illustrate why, we are often unable to determine sex of young fish
Above, is a young Andinoacara coerleopunctatus, cousin to your GT.
Gender is just about impossible at this stage.
Directly below, a mature female tending fry.
Note how the extensions on the paired fins extend about half way to the caudal.
and she is a bit more boxy, than the male in a pic more below

Below the male in full view.
Note the how the fins extend to the edge of the caudal, and how he is slightly more elongate, but has a more massive head.

These basic characteristics hold true of the genus Andinoacara, but do not present or become obvious until maturity.