Why does my senior cat have red belly lumps he keeps licking?

Hi there! Thanks for using Petco Pet Education Center, formerly Petcoach! What you describe could represent nodules or masses. These could be benign growths or malignant growths such as a mast cell tumors, carcinomas, among many other possibilities. I recommend you have Boots evaluated by your veterinarian for a test called fine needle aspirate which is an easy, quick and pain-free procedure which in the majority of cases will help reach a diagnosis to identify what the best course of action is based on the findings. In some cases, a biopsy is needed for a diagnosis. This will help determine what the best course of action is. Good luck! Keeping my fingers crossed that it is something benign and your boy will be just fine!