I have yet to sex one wrong so far on a adult. On the youngsters it's very typical with the Grey's to be certain coloration and 4 months is too young for a major molt.
Monica before you quote me, please do understand I bred Cockatiels for the past 16 years. I understand with different coloration the dots can vary. With most of what you said and quote are from text books and such. I went through hundreds of Cockatiels, not just a few. I have 7 babies with me right now to add to the list. I have never DNA sex any of my birds and I've been 100% accurate on sexing my adult tiels otherwise there wouldn't be any babies. Once the youngster gets to a certain age, they will show what sex they are if your not able to tell by the dots. While young females can be vocal but they have nowhere the singing ability of a male. If you raise them long enough you can tell the difference between a male and a female chirp.
Mike, although I realize that having cared for birds and my research with them for half my life doesn't compare to the 16 years you have been breeding cockatiels, it still doesn't make me an idiot!
I was only mentioning about a young (4 month old?), normal hen that had not gone through her first adult molt and did not have the spots all the way to her body. For bird poop and giggles, her owners DNA sexed her, and the results were female. I tried looking up the thread, but it's been so many years ago that I'm not even sure I'm looking in the right place. I just recall that based on her wing dots, most people assumed she was a male.
I am not doubting your information nor experience, only agreeing with you and saying that the wing dot method is not 100% accurate in cockatiels that have not gone through their first molt. Without having experience breeding cockatiels, I would say that the wing method is fairly accurate, but not 100% accurate in young cockatiels. In adults, yes, it's 100% accurate if the pied gene isn't interfering with those feathers!
I have seen cockatiels as young as 4-6 months old already molting into their adult feathers as I have also seen some cockatiels going through that first molt around 11 months in age. I know that diet, when the birds are born and seasons can all effect when a bird molts. (yes, I know, preaching to the choir!)
Since Peps is about 5 or 6 months old, and we don't know if she/he has gone through this first molt, none of us can say for sure! I just know that Casey, my first tiel, whom I had since she was 5 months old, I knew from the start she was a hen! The breeder is the one who gave her the name, and although I never saw her parents, let alone spoke with the breeder, she never did molt out her pearls! And later on, she has laid eggs!
Perhaps what we should be asking is whether or not Peps has started molting, and if so, are the old feathers the same as the new ones? Or do they appear different?
And if Peps hasn't molted out yet, then just to give Peps time to "tell" us what gender he/she is!