My new puppy won’t stop jumping on our elderly cat — how to keep the peace?

We recently adopted a lively 4-month-old golden retriever puppy, and while he’s full of energy and love, he keeps jumping all over our 12-year-old tabby cat. The cat usually just hisses and runs away, but I worry this stress is too much for her at her age. We’ve tried gently redirecting the puppy and using a leash indoors, but the excitement always gets the better of him. Our cat has always been independent and a bit grumpy about changes, so I want to make sure she still feels safe and relaxed in her home. I’m thinking about setting up a dedicated cat-only space or maybe using baby gates to separate them at times, but I’m unsure if that’s the best long-term solution. Has anyone managed to help their young dog and older cat coexist peacefully? What strategies worked to reduce the puppy’s overenthusiastic behavior without making him feel isolated? Would a professional trainer be worth it this early on, or are there simple home approaches I’m missing?