I have 18 layers, dual purpose birds. Mine to go to Freezer Camp at 18 months. I tried keeping them 2 years but it just doesn't make financial sense. I also cull for the very best birds each year. Most years the birds lay enough and I sell enough to cover the cost of raising them. So we eat eggs for free!
I'd like to mention if you are trying to get a good number of eggs, the birds of today do best on layer feed. Keep the supplementation to under 10% by weight of their daily ration, and make sure they are eating the daily ration. Weighing it out is a good way to find out if they are eating well.
Another crucial thing is to make sure they have plenty of access to cool clean water. In the summer, if the water is too hot, they won't drink enough. If they don't drink, they can't digest their food. Not enough nutrition and your egg production tanks. Ever notice how the laying decreases in really hot weather?
Glad to see this post as I hadn't seen any from you lately....