I'm not finding any Caldwells from Scotland residing in Notts in 1871. All the Caldwells there are in the same place, though, St Mary, same as our Geo.
He's still there in 1901, and a George Caldwell of the correct age died in Nottingham district in 1915.
So...we have a rather wide window for the photo. I'd put it in the 1880s myself, just because of the condition and style of the backing. The photo itself isn't very dateable...not by me anyway

Cheers,
C