The more time they take off during the winter and for setting eggs they seem to lay longer. The oldest hen I had (not barred rock) was 7 and still laying when she was not broody. She laid in the winter as well (until setting again).That is quite individual. If they avoid the internal laying death sentence that so many hatchery hens die from (one reason I do not buy my laying stock from hatcheries ), they can lay a very long time. I have two BR hens, both daughters of hatchery stock, so not first generation direct-from-the-hatchery, who are going on 7 years old and they are both still laying. Another one is over 4 and lays regularly. Now, at an advanced age, they do not lay all year long, but in spurts.
My true heritage BR hens are only just over 2 years old so cannot say from personal experience about them. My blue, black and splash Rock hens are 3 years old and very regular layers
I have had a few internal layers as well. It is terrible.
