Different males mature at different rates. Different females mature at different rates. Cockerels normally go through a very long puberty period, usually a few months before they actually become adults. I’ve had some males start this process just after 3 months, some not start until 5 months, some I butcher before I see any real signs of males maturing. Even their sexual organs inside are still tiny compared to what the others have.
The transition through puberty usually isn’t that long for pullets, although they continue to grow in size after their behavior changes. It’s normally closely associated to when they start to lay. Often, about the time they start to lay they begin willingly squatting for males. But I’ve also seen some that refuse to willingly squat for a cockerel or rooster for months after they start to lay. They are living animals with their own personalities, it’s hard to get real specific as to how individuals will behave because different chickens behave differently. Part of how a pullet or hen responds to a male is the maturity and behavior of the male.
Even if you knew the age of the pullets it would be hard to tell when they will start to lay. I’ve had pullets lay their first egg at 16 weeks, I’ve had some wait for 9 months. There are a few clues that pullets might be about to lay. The combs and wattles become bright red, though sometimes it doesn’t take long for them to go from bright red to pink and back again. It’s a clue, not a guarantee. If you check the distance between the pelvic bones the wider they are the closer they are to lay. Sometimes pullets start squatting for a male, or even you, when they are ready to start laying, but I once saw a 13 week old pullet willingly squat for a 13 week old cockerel two months before she started laying. These things are clues that they might be close to laying, not absolute guarantees.
I can understand it sometimes being hard to tell the sex of an older chicken. Most of the time I can tell sex at five weeks but some take a lot longer. Some pullets can look a bit masculine and some cockerels just take forever to actually start that maturing process. If you can post some photos of the one you are not sure about we might be able to tell, but then maybe not. A shot of the head showing comb and wattle development is good, but so is a shot showing posture and legs. Heavy legs and upright posture are signs of a cockerel. At a certain stage of maturity the saddle and hackle feathers become pointed for a cockerel and rounded for a pullet. If a tail feather is curving down instead of growing straight you have a cockerel. There can be a lot of clues but sometimes they are conflicting clues.
