I’m 68 and I had a spinal fusion (4 screws, 2 bars) 11 months ago. I’m in very good shape for a man of 50. I eat relatively well and I do not smoke or drink. A good diet really helps. Get some guidance in this respect.
You can have pretty good arms/ chest/ & gut, with a 28”-30” blow-up exercise ball, a thin full length roll up floor mat, and 2 dumb bells to which you can add weight as you progress . Look-up the range of exercise with these items on Google or get a few lessons from a trainer. Then start slow, and do your exercises religiously 3 times a week. Work up a good sweat. But,do not exercise to exhaustion.

For aerobic exercise, power walking , outside, on mixed hill/ flat terrain, wearing wrist weights ( start with 1/2lb.), will get and keep you heart/lung strong. Get the book “ Power Walking” for details on walking style and progressive programs. Steady progress is the key. Again, walk sweaty, but not to exhaustion.

If you must walk inside , use an adjustable , powered treadmill, rowing machine or an elliptical with arms. The elliptical is the lowest impact. The rowing machine is the smallest, least expensive and best all around exercise. But rowers are BORING I/M/O. Upbeat music or TV helps with boredom and provides motivation.

I work in a high stress professional environment. When I gave up using liquor and tobacco as tranquilizers, going to the gym became my physical and mental lifesaver. Working up a good sweat is a great antidote for a day when, “...the bear eats you!”

Remember, you are not competing with or comparing yourself with anyone else. If you get past the first 3-4 weeks and start to feel and see the difference in your mind & body, you likely to get hooked ona healthy regime, which just keeps getting better and better.

Good luck.