There are a lot of variables that make this a very hard question to answer. Confined or free-range? If confined, what kind of confinement? Climate? What does she eat? Kept with extra light through each winter or not?
I have an older BO hen, she's at least 5, may be as old as 7, I'm not sure when I got her. Last year I was sure she wasn't laying, but now I think I was mistaken. I'm 99% sure she's laying now, and I've seen her being mated lately. Her comb looks a bit washed out, like they get when laying, and her legs are pale. Plus, one of the younger hens from last summer looks almost exactly like her, only a touch of black in her tail and neck, and none of the others hens could be the mom, colors are all wrong. None of my roos from the last season would account for it, either. The eggs I collected to hatch, except for a few I segregated to collect, are from random hens, no idea who laid what.
I once had an old red hen, probably a NH, but I'm not sure, who laid right up until she died, (I found her on the nest where she'd been laying her eggs) about 7 years.
If they get more protein than the usual 16% layer feed, (which, IMO, is a minimum, not an optimum, amount of protein for a layer) they lay better, and possibly longer. I know they quit when they run out of eggs. But they can quit before they run out, if they aren't getting what they need to keep laying. Black oil sunflower seeds help, too. Not too many, don't clog their systems with too many shells, but a little sprinkle with the feed every day helps.