How long do hens lay eggs ?

[JackieinYorktown]

I am hoping that it is for more than one season, as we are all getting attached, I have 17 hens that are assorted heavies (Buffs, Wyandottes, Rocks, EE, etc)
I know that they start at about 20 weeks. When does production start to drop off ?

 

[speckledhen]

Duplicate thread...please no cross posting, per BYC rules.