In another thread I tell about the finding of a stove pipe flue cover like this one the SO discovered when she took down some drywall.
Does anyone know when it was made?
These were used up until about 1930. Probably not much later. So anytime before that. How old was the house?
The house was built in 1934. It’s location has been a holiday destination for decades, and the house was probably a place for get away to in Summer. It’s been added to over the years, and I don’t know its original configuration. I think maybe the latest addition was in the '70s – though the curtains looked like they were from the late-'60s. 
I’m pretty sure the bathroom was where it is now, sometime in the late-'60s or early-'70s judging my the wallpaper that’s been uncovered. So just a WAG, that chimney may have been in use through the '50s. Of course, flue covers can last a long time after they stop making them.
They still make them. There was a beat up one in my house when we moved in. The pattern on the plate in your OP is different from the Fulton. The manufacturers may have had design patents on the plates and you could use that to figure out the manufacturer if you can find another plate with the same pattern.
I’ll retract my earlier contribution. My grandmother still had that kind of cover up until about 1955. So, 1930-1955.
That was supposed to be a link, not bolded.