KarynVA
Crowing
No. You have nothing to worry about.
Each bird is different, each breed is different. They aren't unhealthy because they don't lay perfectly on time.
I've had birds take as long as 8+ months.
I agree. It's definitely not an exact science and all chickens have their own puberty timeline, just like people do.
This article shows photos of chickens' wattles during a 3 week period just before laying, and has other useful info about when they may be ready to start laying:
https://homesteadandchill.com/when-chickens-start-laying-eggs/