Hi @newbeginner,
Thank you for your question about tiling over old gyprock.
Assuming the gyprock is still structurally sound, and it is just damaged paper, you should be fine to tile over the gyprock. If the internal gypsum is fractured and broken, it is likely better to replace the plasterboard before tiling.
If you had any photos, I'd be happy to take a look and offer my advice based on them. Let me know if you need a hand uploading images, I'm happy to help.
If you're confident that the gyprock is still structurally sound, start by addressing any low points by giving them a skim coat of Gyprock Multi-Purpose Joint Compound to give a nice even surface.
It is then important to use a primer such as this Davco Ultraprime to increase the bond strength of whatever tile adhesive you choose to use.
You might like to check out How To Tile a Bathroom Wall for some guidance on the tiling process.
Let me know if you have any further questions.
Jacob
