My chickens are 21 weeks old. How long does it take to tell their sex at the latest?

[JuliaSunshine]

I have 12 Light Sussex (heritage dual purpose breed) and two of them started to look like cockerels and crow since week 8.
Now at week 21, they are the only ones that are definitely roosters and I'm not sure about the rest.
Some of the 10 chickens have a bit bigger comb, wattles or thicker ankles than others but no one developed any rooster hackle or tale feathers. No crowing either.
2 or so of the 10 started to lay eggs a week ago but more could be laying in the bushes without me knowing. They're still in training.
How old should they be for me to assume that they are all hens at the latest?
Thank you!

 

[TheOddOneOut]

This is a good age. Post photos and we can tell you.

 

[SilverBirds]

They are definitely old enough to sex. Post pictures when you can!

 

[JuliaSunshine]

These are two who have the biggest wattles among the 10.

 

[JuliaSunshine]

 

[Sussex19]

They are both pullets, and look like they should start laying soon!

 

[JuliaSunshine]

They are both pullets, and look like they should start laying soon!

Thank you! It's still hard to believe 10 out of 12 are pullets but it's much better than 10 being cockerels thank goodness.

 

[SilverBirds]

Pullets!