It not unusual to see no bone growth at six months. Usually you will see SOME bone growth at about a year -- but this is a very SLOW process. So try to be patient. I know it's hard, but at his age it might be a bit slower than usual. It's good that he's in good physical shape and doesn't smoke -- that's great. But still as we age, the process slows up -- so just be patient.
I wish you the very best. Please keep us posted on his progress, will you? I hope so. God bless and take care.
Hugs, Lee