That is a beautiful Texas, looks like a badass lol, but size and lack of a hump are not a sexing method. Not all males reach over 12" just like not all human males reach 6 feet of height, even though it's entirely possible and pretty common. The size of your tank and maintenance schedule might have played a part, but it's ultimately determined by genetics.
Females have a black blotch on their dorsal fin, this can be kinda tricky when they're young but it's a very reliable sexing method for adult fish. You can also vent it to be 100% sure.
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