I can't say how back this kind can be documented.
I copied it from an original rifle, but it was English, and I would guess it dated from the 1850 (or newer) era.
As far as how far back peep sights can be doucmented, I can tell you.........A LONG WAYS!
I have seen and handeled cross bows with peep sights that date back as far as firearms do, and perhaps farther. I also have seen and handeled Jaeger rifles from the early to mid 1700s that had peep sights. Most were a standing type sight, mounted on the wrist of the rifle.
There are some old American flintlock arms I have seen that had simple peep sights on them that probably date back to the late 1700s, but it's got to be kept in mind that such sights could have been added after the gun was made, so all we really have to go on is our best guesses. Some of the sights I have seen are very obviously OLD, but how old is not known. (at least not known by me)