Cockatiel gender is reasonably easy to pick visually, but it will depend entirely on how old your bird is and whether s/he has gone through their first big moult into adult plumage or not. The best indicator is to look at the underside of the tail feathers, as a male will have solid colour there whereas a female's tail feathers will always retain a rippled/stippled effect of colour on the underside, like that illustrated here ...
Thank you!Yep well if they're adult feathers then that would indicate you have a little hen on your hands π The paler feathers show the barring in an adult female too, though you might have to wait until they're moulted out and hold them up to a bright light to be able to see it.