when they grow, and when they dont

[lorilaa2]

I have several of what I think are young roosters all hatched at the same time but some have never crowed, why is this? I am trying so hard to figure them out. They don't look like pullets or act like pullets, but.....

 

[olijo123]

How old are they?

 

[lorilaa2]

they hatched april 10, some have been crowing for wks now, a couple have not.