The older they get, the more they slow down as far as laying. My only BO quit laying at 2.5-3 yrs old or so, and is now nearing 5 yrs old. But we have room for retired layers so it's not an issue for me.
Since egg laying is important to you, best to sell or eat the existing birds. Then, depending on how many eggs you need and how much space you have to work with, start building a new flock with some sort of plan for staggering ages if at all possible, which will give you more consistent egg production over time.