Welcome to the Bunnings Workshop community. It's marvellous to have you join us, and thank you for sharing your question about painting your limestone walls.
Limestone is a porous surface and that means that if you paint over it, the paint will enter the pores of the stone and will become impossible to remove. The paints longevity will depend on its location and exposure to the elements.
A good example would be a painted fence. If part of it is under the shade of a tree the paint on the fence will often last longer compared to the part of the fence that is exposed to full sun.
In order for us to give you comprehensive advice, would it be possible for you to post a photo of the location of the wall? This will give our members a chance to assess the wall's location and condition. We can then make recommendations on how to proceed.