With this colour variety (rosetta tuxedo - I love the rosettas) you can't tell unless you try vent sexing. I had no luck with that until mine were mature. You can listen out for males crowing or watch them for behavioural differences. Males make a low grunting noise, only the males crow and only males will mount another bird (whether that bird is male or female doesn't matter to them). Males will also tidbit treats for the females but all that only happens when they mature. Mine didn't mature before winter (I'm in the southern hemisphere) so I had to wait for spring to reveal all. Hope that helps.
