Look at Diabetes and exercise by Stanford Health Care
This is a short summary of what they say, but they also show exercises for seniors.
They recommend 30 minutes moderate exercise 3 to 5 times a week. How hard must you exercise? You must still be able to talk and maybe be a bit out of breath.
How to safely start
1. Think of where you are in your fitness.
2. Find a buddy to exercise with you. Sometime you need to be push in committing yourself for their sake.
3. Let your body dictate what you can do.
4. Make attainable goals e.g. how long, how frequent, what time.
5. Start with 5 minutes out and 5 minutes back.
6.If you are fatigued, take a nap.