It's only an indicator if they're specifically bred for those genes to be sexlinked.Mine are 6 days old. I have 5 pullets (hopefully). Only one, a buff Orpington) has tail feathers.
I’ve heard feathering out faster is usually a sign of a pullet, but most pullets don’t have tail feathers at a week old.
 
	 
 
		 
			
		
		
		
	
	
			
		 
 
		 
 
		 
 
		
 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		
 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		