I swore Newman was a female at first. He was dropped off at a pet store by a girl who was allergic, so I really didn't know his age, just that he was young. The girl thought he was a female too, and named him Sweetie. Well, his color changed quite a bit since I got him 7 years ago, I can now tell that he is a male, and he talks all the time.It looks like a female to me. Female cockatiels have lighter orange cheeks and little yellow on their head, while the males have a full yellow head (for normal grey cockatiels). But if it's still very young, it can turn out to be a male.
The only way to be 100% sure is DNA test
i agree with LoveMyParrots, and its a myth that female cockatiels dont talk as well they talk just as good as males! she/he is very pretty!
It can be hard to say why a cockatiel is making a particular noise without being able to see everything that's going on around the bird.
There is a theory that you can sex a cockatiel by the wing spots when at a young age. It's not 100% accurate, but it's a 50/50 chance. At a young age, males supposedly have spots on their primary flights and secondary flights are clear. Females on the other hand will have spots on primaries and secondaries. As adults, males lose their spots and hens lose the spots on the secondaries.