At what age do hens stop laying?

[Alvordhens]

What breed did you have that layed often at four years old?

 

[hunt]

I have about four to five hens laying right now in total I have about 28 hens so I know some of them are to old to lay but there are no feathers in my coop.All of my hens are mixed breeds and mixed ages so I don't really think that all of them would stop laying at one time!