This whole discussion reminds me of why I retired out of raising hens for selling eggs. It was one of the "talking points" I listed when we finally decided to sell the farm and completely retire. I now live in a small farming community with lots of others who keep chickens (and sell me eggs)...
From my observations it varies by chicken and breed. I had a Orpington that laid until age 6, was about 1 egg a week and sometimes 'weird' eggs but she kept on going. Her sister quit at age 3 and was the cranky ol' lady of the flock. Ruled my flock for 3 more years as everyone's stern granny. I...