Paint peels for a number of reasons.
When your home was originally painted the best paint may not have been used or a sealer may not have been applied beforehand and now after many years and many coats of paint the weight of the new paint is actually dragging the old paint off the walls and ceilings.
Ceilings can also stain and peel if your roof has cracked tiles and you have water leaking into your ceilings.
In particular paint can peel from ceilings because the old calcimine ceilings need to be washed, prepared and sealed properly before repainting.
Sometimes the gyprock can be too high in acidity or alkaline content and this can cause the paint to peel off the walls or ceilings constantly.