Hi there. I have a 13 yr old female cat who is prone to having warts on her back. About 4days ago, I discovered a hard lump on her back near the spine area. It seems to move with the skin, but is way too big and hard to be a wart. Could anyone help tell me what this might be?

13 years old, eh? It's more than likely a fatty tumor, they're pretty common as animals get older. If it suddenly sprang up, or gets markedly bigger in a short about of time, then you might want to take her to the vet. Most vets won't do operations on benign tumors on older animals as it just creates unneeded stress on the animal.