As noted, pain and other stress will likely crank up blood sugar. And, as already said, pushing too hard in the gym is a good way to hurt yourself in various ways. You are making some changes that take time. As for exercise, concentrate on improving your cardio as you start, because it will help your body deal with the stresses that come with other forms of exercise, and along with diet will help you cut weight, which also help with the BG stuff. You don't want to push so hard that you have an MI on the treadmill - I hear that is counterproductive.
There has been a falsehood out for many years that we are going to add weight as we age. We MAY, but we should not. Muscle weighs more than fat, and most normal people (not super-jocks, a group by which we mere mortals should not measure ourselves) will lose muscle a bit at a time as we age. As a result, even staying steady means we are likely adding fat, especially after we cross 50 or so (like me)
. I have also had to lighten up my lifting, going back to lighter weights and more reps, because my joints (especially my shoulders) have been screaming bloody murder.
I used to start lifting with a weight I could lift in good form at about 4-5 reps, then work down about 20% at a time to a final set at about 10 reps, preferably in 4 sets, with as little rest as possible between sets. I would often do this after running a substantial distance. A short run was 5 miles, and I was not above 9-12. Those days are gone. Now that strength and mass are not as important as when I was still in LE, I don't need to, and the drawbacks had to be considered. If/when you start into resistance training (which is part of a comprehensive fitness plan), don't be concerned about doing weights light enough to do 12-15 reps in good form. Even if your muscles can handle more, your joints and connective tissue may have some harsh words to speak until they get more able to deal with added weight, if they ever do. Don't be afraid to spend the money to get a good assessment from a real fitness trainer if available at your gym. We make lousy lab rats because of the variation in human bodies and minds; lab rats and mice are bred to be as identical as possible.
I see folks well into the 60s and 70s, and some I suspect are in their 80s, at the gym. Most of them do "modest" exercise because they are not trying to do marathons, power lift, etc. Regardless, they are taking care of themselves, and are probably "younger" in net effect than their actual age. There are a couple old guys who have been doing heavy stuff all their lives and whom I would not arm wrestle on a bet, but they are in the freak category, and you do not want to compare yourselves to them.Walking the dog can be good for both of you, my research with the house hounds over the years convinces me that a tired dog is a good dog anyway.
This is NOT an overnight process. It is a longer term evolutionary process, especially considering your description of your prior exercise history. Get in it for the long run, find ways to enjoy what you are doing and not just its benefits, and I'll bet that in 3-6 months, there will be some real changes that you don't perceive until measuring them.