score:4
It is a Russian uniform.
The cap itself and the oval cap badge give it away:
A Prussian hat would have two round c**kades.
His shoulder decoration further implies that he was a musician:
src: Staff Trumpeter of a Russian Line-Infantry Unit, 1900's.
Unfortunately, the peaked cap was in service in that basic style for quite a long time, and certainly as early as the Crimean War:
But the fine facial hair style might indicate (to my personal opinion at least) a much later date. My guess would be 1900–1910, 1880 the earliest. Minimally supported by comparing the colour plates in — Boris Mollo & John Mollo: "Uniforms of the Imperial Russian Army", Blandford Colour Series, Blandford Press: Poole, 1979.