I have 54 egg layers. Most are over 2 years. Yes, egg production decreases with age. But some hens continue to produce well long past that 2 year mark. It depends on the bird.
I have two coops, (see my BYC webpage), One for meat birds, one for layers. I use a section of the garage as a brooder.
My large coop is divided down the middle so that I can have adolescents growing out while my layers are doing their business and getting to know them, through the fence. I currently have 106 4-week olds in the grow half. Only about 80 of those are going to make it to the layer side. A few roos are mixed in the bunch, and will be sent to the little coop to live with the spring meat birds until butcher day.
Each spring, I spend 3 days sitting in the coop, marking who is still laying. The others go to freezer camp.
So, YES, I say either have a very large split building or two separate coops so you can optimize your egg laying.