My dog Daisy had a Grade 4 luxating patella and needed surgery around the same age. She recovered very nicely - it took about 2 weeks of cage rest and increasing activities after that.
My dog had her evaluation and her surgery by a board certified ASVS veterinarian who specialized in orthopedics. You can check to see if your vet is ASVS board certified by visiting
www.acvs.org.
I will note that my dog also has a grade 3 luxating patella in her other rear leg and although it goes completely "out" from time to time, my vet will not do surgery on her UNLESS she becomes COMPLETELY lame. So, when it happens to "go out" and I see her hobbling, she goes on pain medication and cage rest until she is back up and around.
This is a very common issue in the breed and surgery is sometimes necessary but you should make sure your vet takes a conservative approach if your dog is not lame.