You've got 2 things: the injury, and then the age. Your main goal should be avoid re-injury.
Spinal injury - That's hard to deal with. It's going to depend a lot on what disks got injured, and how it's affecting him now.
I would start with a gentle warm-up. For skill work, start with landings, and 2 hand vaults. The idea is to slowly give him some tools he can use in real life. Give him lower impact moves where he is in control the whole time - avoid the kong at first. Have him constantly monitor his body.
As a climber, he's probably going to have a good balance of upper and lower body strength. Flex, power and endurance should also be good. This will all be modified by how his injury affects him, and how long he's been out of training.
Depending on his attitude... if he seems cautious the first time, that's good. If he's gung-ho and charging... rein him in the first time. As an injured athlete, you don't want him pushing it, gutting it out, and hurting himself. Older people heal slower, and re-injury is junk. Also, some times we know what we COULD do, and it's frustrating to be older and not able to do what you could a few years ago. As you get to know him better, you'll be able to know if you need to encourage him, inspire him, rein him back, change exercises, whatever.
