Sexing cockatiels....delayed dimorphism

[Grey_Moon]

My cockatiel Sully is about 5 now---and although he's never been sexed he's to everyone's best guess male (he whistles, struts and taps his beak on things).

He's a pied split to something (grey i think) so I know the visual sexing can be tricky if not impossible.
I was pretty sure he was a male as a baby (he had bright red cheeks) but for four years he had bars on his feathers under his wings and tail so the vet said female.

At age 5, those bars are gone. He molted them out more and more at every moult but he began to do his typical male tiel behaviour at about 1-2 years of age. I'm a little confused though, seeing as I didn't think it took cockatiels this long to molt into their final colouration seeing as they become sexually mature so early. Did he take so long to mature because of the stress of the giardia?
I'm hoping to avoid having to sex him DNA-wise.

Is it possible? Could anyone think of why this happened the way it did? I'm assuming/pretty confident he's male, I'm just wondering why he had bars for so long under his tail and wings.

[zazanomore]

Einstein had one last tail bar feather until just a few weeks ago when they all went through a molt. He's about 10 months old.

I'm no vet, but maybe birds just mature at different rates.

Though it is uncommon, some females will sing just as good as males.

The only way to really know the sex of your bird is to get him DNA tested.

[Kim S]

Pied cockatiels are notoriously difficult to sex by appearance. But if he has coloured tail feathers you should be able to tell. The tailfeathers never lie unless they are pied as well (but then they are just blank and not saying anything).
I would like to see some pictures though. I might be able to help out.

The changing of the feathers is related to hormones. Starting to display sexual behavior at age 1-2 is also quite late. I think the Giardia might have something to do with it.
Half of my chicks have a distinct male or female behavior at the age of 2 months when they are ready to leave. Almost all of them display the behavior at six months. It might take them longer to start whistling though.