I'm 51 and prone to back issues, knee issues but I make it work with other forms of fitness to compliment kiting. I find the best non kite thing to do is swimming. Plus it helps where we kite - with certain wind directions we are in deep water and may have to swim a bit. Other than that it's core strengthening exercises and cardio. As far as kiting goes strapless is best for me on my knees. When anything goes wrong no knees to jar.
For me it isn't all feather landings when I jump with a Twin Tip. I'm getting better at it and recommend a kite that lands the jump smoothly. From what I read the Edge, NRG, foils have more hang time...
The worst injury I ever got kiting was throwing my back out when I was bending over rolling up the kite after a cold water session. Now I bend my knees
The 2nd worse was getting thrown around backwards after hitting a wave face on the way out in 7m conditions. Flew up pretty high but twisted somehow. The kite got out of control, I must have pulled down on one end of the bar and I looped the kite. Before I knew it I flew backwards towards the beach and took the brunt of the crash with my head and neck. Luckily I was in 3 feet of water. I think I had a concussion plus I had whiplash for a few days. I should have released
Now I never end up in that situation. I will always remember that crash! I always do my fun stuff in deep water. You will not find me skimming along in 6 inches of water.
Oh yeh get good quality safe gear. Most beginners I see getting hurt are either on crappy gear or in shallow water...