Have you had a consult with an orthopedic surgeon? That would be your first step. General practice vets are good for diagnosing a CCL tear, but when it comes to surgical repair, you really need to consult with an ortho specialist. TPLO might be the best option for your dog, but extracap can work too. 7 years old is a good age, not old, but not crazy young either. So if your dog will be ok with strict exercise restrictions and won't try to do anything stupid during recovery, the extracap could work. You know your dog best. If he is overweight at more than 100 pounds, you need to start trying to get some of that extra weight off too. It will only help.
My 4-year-old dog has had both of her knees repaired. She had TTAs on both. Similar to the TPLO, but they cut a non-weight bearing bone instead of a weight bearing bone. She recovered beautifully both times. I know the idea of the TPLO is scary, but if your dog's knee is unstable, surgery is the only way to stabilize it without further damage.