Actually;
baby frills can be sexed. Examining the tail base will tell you if the animals is male or female in many cases. After 3 months of good growth then the tail becomes too thick and you cant tell until closer to a year. So when people tell you that a young animal is female then they would only know if they sexed it as a baby. Not many people do this technique; especially here in the US. Coloration on the chest is not a good indication of sex. i have females that are blood red chested. If you have multiple animals in a cage then you also need to consider stress. Unless your growing them up indivdually and kept them on good diets then your not going to kow for a while.
In general square head means male; even on smaller animals. Frill size is not a good indication either; as females will have large frills for their size.
good luck,
miz
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Mizzy: frilldragon.com