Unless of course it has been redone in the intervening hundred years. Lime plaster is usually off-white and very thick. Laths were used for ceilings and partition walls of studwork. Frequently cracked and loose. Lime plaster was also used direct on brick walls, where it is likely to be in better condition as it does not rely on wood that may have rotted or shrunk, nails that may have rusted away, and nibs that will have broken off due to wartime bombing shaking and movement (the reason why L&P ceilings are liable to fall down at the slightest provocation). If you have a teenage daughter she might bring them down by slamming doors.
I can't see your green but it is quite likely distemper. A durable "paint' made of glue, ground chalk and pigment. Usually in pale pastel colours due to the high content of chalk. Very difficult to decorate over. Recognition is that will not wash off in cold water, but can be washed off with kettle-hot water, whereupon it has a distinctive unpleasant smell, due to being made with the boiled-up hooves of dead horses.
P.s.
No, you can't paint it. The paint will fall off. This is characteristic of distemper, not the plaster itself. You can scrub it off with boiling water. Or use lining paper, which is easier.
