Welcome to IronMagazine!

What's your height and weight?
I'll be 49 in August but can empathize with the tendon deterioration at least a tiny bit. Was taking the steps two and three at a time at the elementary school where I teach. Next day? Felt like I had broken glass in my knees. Was wondering what I had done and then thought of bounding down the steps.
Joked with friends that when I'm 99 the bones will just fracture outright.
Congratulations on hitting 79 and still being interested in strength and muscle.
I'd get blood work done if possible, get a good trainer, read Built's
beginner info (see link in my sig), take into account the fact that you are older while maintaining a positive "I can gain muscle!" attitude, and get on a set eating schedule.
Is your diet restricted due to your ilo (however it's spelled) or do you have the green light from your doc to eat as you see fit? Are you structurally restricted at all or do all your limbs/joints bend as they did years ago?
Can you do seated leg press on the machines? Squats might be out from your back surgeries, but the leg press might be an option? You want to work those compound movements as much as possible and leg work is a great goal.
Wishing you success! Please keep posting. Have you created a training journal? One member of this site you might seek out is Burr. He's 69 years old and is a terror!
Burr's journal:
http://www.ironmagazineforums.com/online-journals/113982-burrs-wonderful-workouts.html