A good question. Eley's certainly listed it as a pin-fire option by 1874 and I can find an Eley reference to making them in centre-fire sometime between 1861 and 1874 which is about as early as you can get a centrefire. My guess is that it followed on from 28 bore muzzle loaders and with Gunmakers having tubes in that size chambered them for 28 bore pin-fire when breech loaders came in and that naturally led on to centre fire options much in the way of the other odd bore sizes such as 14's, 24's and 32's. In short it is as old as the rest of the centre-fire clan.
The earliest Kynoch listing I can find is 1882 and that in centre-fire only. The British standard then was 2 1/2" (still widely available here) with a load standard of 9/16th. ounce of shot. Lagopus.....
