My Comet, a "red sex link", started laying at 18 weeks.
A red sex link is half Rhode Island Red. The other half can be a line carrying the silver gene I think, to make red female chicks and white male chicks. So the red color is linked to the sex of the chicks and it matters which parent is red - I think the hen must be red. Not all color genes are linked to male or female.
The one parent is Rhode Island Red, and the other parent can be White Rock, Delaware, White Rhode Island, White Leghorn, Silver Lace Wyndotte. May be others. The hens grow up red with some white underfluff and/or some white tail feathers.
If one parent is Rhode Island Red, and the other parent is Barred Rock, the chicks are Black Sex Links. Can also be sexed at birth. The hens grow up black with gold around the neck, and roosters are barred black.
Depending on line and mix, the Red Sex Links have different names like "Comet" "Indian River" "Red Star" Hyline Brown, ISA Brown, Cinnamon Queen, Hubbards, and newer names every year. Some names are registered trademarks, some are fanciful names given by the hatchery. I think Comets are patented by Hubbard, which company is big in chicken genetics. Sex links are not a breed, so one cannnot make more by mating a red sex link hen to a red sex link male - the chicks inheirit different gene percentages and aren't exactly like the hen.
Rhode Island Reds have always been very good egg layers. Over the last century they have been intensively bred to lay more and lay earlier. Some lines are called "Cherry Eggers" and "Production Reds." (some might have had leghorn added at some point.) Production Reds can be mated and the chicks are more Production Reds.
I wonder if Fayoumi may have been added at some point to trigger earlier laying as they mature at 14 weeks. Many Fayoumi were used in research at university research programs. Laying at 18 weeks is much earlier than traditional heritage breeds which lay at 24 to 32 weeks, some even later. Which I wonder if the earlier laying gene came from Fayoumi because the difference is so dramatic - a four and half month wait versus a six to eight/nine month wait. If anyone knows more about this, I'd like to know for my research.