For commercial detectors, I write them down or recommend replacement when you cannot test the sensitivity on them. Smoke Detector Sensitivity has been looked at a lot more in recent years here, and the fire inspectors want them on the reports and any detectors replaced that cannot test for sensitvity (IE, the Edwards 6249C). For smoke alarms, I write them down or replace them if they are 10 years or older. As well, has become a thing for the fire department. The one condo we started servicing, all had smoke alarms from the 80s. Needless to say, before we could replace them, the fire department had a surprise inspection. & They went and replaced every single detector that was from the 80s or out of date.
I mean IMO I don’t think there is a shelf life, like the old extinguishers. They require replacement or recharging after 6 years, but they’re still good, I keep expired extinguishers around my house. But I just go by what I know from working in the field.