Will our tibias really get separated and there will be a real gap in the middle or it's still intact but just broken.
Complete osteotomy, meaning it's a clean break all the way across. Distraction osteogenesis wouldn't work so well otherwise. Here's a
non-gory animated video. Here's
a bloody one on a real patient for those that are OK with it.
Not as scary as it used to be, since we used to use saws. But hey, you're under general anesthesia anyway.
is there any way the legs will be nearly as strong as the original for athletic purposes?
Sure, but give it two years for complete consolidation. You'll have to rebuild muscle as well, so you'll definitely feel less athletic for a good while, all the while aging as well. Ask your athletic friends who have broken their bones.
how old is the oldest to do this surgery that's still worth it?
Very subjective. I've seen plenty of men over 60 getting hair transplants. Many are married and retired, but they wanted it for themselves. CLL is obviously more invasive, but the message is that you do it for you. We've got guys on the forum that's over 40 doing CLL and they seem happy.