Best bet is to provide the youngest age photos you have as well as current, and indicate the age at the time of photo.
I have been able to attain over 80% accuracy when sexing my own poults in the first week, but after a couple of weeks until about five months, it can be a challenge. My success is because of the sampling size. If I have one, it's a guess. If I have 20, I can sort them by various characteristics (head shape, foot size, shank size, snood size) and see which box they best fit. There will always be some with conflicting characteristics.
Once they start to mature, you can check the pelvic bone spacing. Males have very tightly pulled together pelvic bones under the vent. Females have some space between the pelvic bones.