Okay. I'm a PT who has not seen you in person. Take this with for what it's worth.
Your healing time will depend on several things. Numbers one and two being how large the tear is and how long it's been there. Your doc should have a reasonable feel for this from your MRI and physical exam.
You are not going to heal nearly as well at 67 as at 27. Not that it won't, but you will need to be patient. Being super active helps. Hopefully your overall health is good, don't smoke, etc.
As for the stem cells, I do not seen them used in RC repair in my practice setting. I'm sure they are in certain situations, but in my opinion they might make a low single digit difference in your healing. If you don't mind the cost it's not going to hurt.
You will be better after the repair in the long run. It's also better to fix it sooner than to wait until it's really gone and it might not be able to have it fixed at all.
Good luck