Yes, it is German and I suspect it pre-dates 1900. Ok, we're going to need some help from you. The rifle needs to be taken down and pictures taken of the proof marks and any other stamps that turn up. Most will be on the bottom of the barrel just in front of the receiver.
As I cannot see any kind of magazine protruding below the stock and it doesn't appear to have the typical bottom metal I assume this is a single shot rifle?
I can't find the exact model I was looking for but I believe your rifle is at least based on the 1888 Commission rifle, which was more Mannlicher than Mauser. I have an 1890, (I think), Haenel/Rasch sporting rifle that is similar but, a search for that model turned up nothing like yours or mine.
