I bought a 50 year old house it has a green board in the shower cubicle,no tiles. Can I paint over the board?

What type of paint can I use on the green board in the shower cubicle? Does anyone suggest marine grade or other? I don't want the paint to peel off from the hot water hitting it. Can someone tell me what type of board this might be? The house was built in the 1950s,60s. Could it be fibro or asbestos?