My girl is about the same age and no eggs, but we didn't get our 1st eggs around here until they were about 30 weeks or so, those being from a wyandotte and a white leghorn. when the time is right it will happen.
I am in the same boat. I have 15, 24 week olds and no eggs! To make things worse the one rooster that snuck into the pullet order is a jerk and attacks me everytime he gets the chance. When I went to the grocery store yesterday I bought 4 packages of raw "natural" chicken and a roasted chicken, to the sum of $35+..... Not to mention the 2 dozen "local" eggs from another state. I am really starting to think something is wrong with this equation.
I have a group of Columbian Rocks (LF) that are 28 weeks old and no eggs yet either. I think we are fighting the decreasing sunlight daily and that is part of the issue.
I also understand that where your birds came from can effect laying as well. If your birds came from a "breeder" of SOP quality fowl, they just might not lay until next Spring as they have the original instincts of the breed to not lay until it is "chick rearing time"...hatchery type bird have been bred for egg production and therefore should start laying sooner