I think wristwatches didn't really catch on until after WW1 (late 'teens, early '20s), so that is probably the oldest it would be. Of course, it could be later.
I think more 20's to 40's time frame. Probably too far gone to get an ID on maker... The works were almost generic, the cases set them apart. Unfortunatly the case and glass are long gone. All you have is the back case. The front cover would help ID it quickly.
DG