Weekly physical activity plan for a deconditined 64-year-old?

See your doctor. It would be best to see your doctor for a baseline physical exam first. At that time, he can outline a plan that would be in line with your capabilities. He can also outline a balanced diet for you. Apart from this, mild to moderate physical activity, like walking and possibly easy swimming 2-3 times a week would likely be more than enough activity for anyone at this point in life.