Oldest? My roo, or maybe hen? is about 20 months old
I'm sure he's a roo, but I have had two judges and one of the best breeders tell me they are sure he is a girl. He doesn't lay, & he does crow.
Other than that, Daphne became Daffid at about 10 months--he pretty much bloomed from pullet looking to cockerel looking & crowing almost overnight. Lil'Bit was 13 months old before she laid an egg. I was thinking/hoping pullet, but not certain--no truly defined characteristics. I showed Cirrus as a young pullet in September and a year and a couple of weeks later he had bloomed into a Champion Bantam cock!
Oh, and the youngest was a 4 month old PQ silkie who took over and brooded a newly hatched chick, then once he was raised went broody on other girls' eggs. After those babies were raised Qurious finally laid her own first egg.
My white silkie is about 4 1/2 weeks and honestly, I think I'd keep it even if it is a boy cause we just love "it". I just hope if it is a roo that the crowing isn't too loud or my neighbors are gonna kill me.
How old are they, and can you post photos? Some varieties are easier to tell at a younger age than others. Partridge, for example is usually a variety that you can tell pretty early. Of course my mystery bird is a blue partridge.
But I have a pen full of 3 1/2 month old chicks and I can make a pretty good guess on many of them.
My boy/girl is a 4 1/2 week old white silkie. No sign of a comb on top but I know that doesn't really mean much at this age. I figured I would know by the time it is 4 months or so...or at least I'm hoping.