hello
your not alone, I have 5 black rocks and they were 21 weeks old on Monday. 3 are starting to get visible red combs etc but 2 are still not really showing any signs and none are laying!
tried the marble eggs in the nest boxes but nothing yet still. They have also started to prefer the nest boxes to the roosting bars which is annoying only from the poo in the woodchip perspective and is a new thing as before they happily stayed on the roosting bars.
Still...as long as they start to produce soon otherwise its the cook/chook pot/s for them!