wing feather sexing

[Nigellas]

Is it an accurate was to sex a bird? For instance, is the brown easter egger (on the right) in theory a boy, as the wing weathers are much less developed than the lighter one on the left that has more feathering?

 

[LittleLady98]

Some people do tell the sex by the wing. But the EE in the pic, is "he" younger than the others? Because the wing development depends on age.