I've never known anyone who could stay on a keto diet, because it is inherently unbalanced. If you like fruit and bread, try vegetarian or vegan. I've been vegan nearly 5 years, and my only regret is not changing sooner. Cheaper and much healthier.

Definitely start slow and build into things. About 4 years ago I also started working out again regularly after about a 10 year hiatus. I started with 2 days a week, and now I train 4-6 days a week again. At first my body (particularly my tendons) needed 3 days to recover between workouts. Now I can work out any muscle group 2 days later and I'm (usually) fine.

Once I had the habit of working out nearly every day, even our long lockdowns couldn't keep my from finding a way to train. That's how I got back to being a lifter and not just a golfer or boxer.