I'm a recent Betz patient. I don't think age is a problem with Betz. Even at his age he is: energetic, strong, sharp and will stay until every question is answered. I think the issues with Betz is that he over exaggerates things and he tends to ignore you once you leave Germany. I sent him xrays more than 3 weeks ago and I haven't gotten a reply. Luckily I sent the same xrays to Paley & Assayag at the same time and got prompt responses from both the next day. I think if something went wrong while lengthening in my home country, I would have been screwed.
Betz Institute is transitioning from Betz to Dr.Becker. From my brief encounter with Becker he seemed to be a nice guy. Sounds like he's been training under Betz for a few years. However its hard to gauge how good he'll be once he starts doing this on his own.
He could be an exception then if he is as energetic, strong and sharp as you say at 72.
As for the other doctor, is he also a cosmetic surgeon (doing non-ortho surgeries)? If so, that is a bit of concern. I have never seen an ortho surgeon do non ortho surgeries anywhere. And to add to it, LL is a more specialised ortho surgery. I think even if you spend all your time on it as a surgeon, it will not be enough. Many LL surgeons probably wish they had more time to do some research, write some papers, take on some other patients, teach other surgeons, attend conferences.