If you feel tired or stiff stop after a few minutes. However, baring illness or injury, give yourself the five minute test. Begin exercising each day and see how you feel after five minutes. The first five are the most difficult. We have to learn to conquer inertia.
Old habits hang on.
You will find that the hardest part is getting up and starting. Once you are moving it gets easy. To strengthen your exercise habit, set goals and reward yourself for your achievements. Set modest, easily attainable goals such as walking for thirty minutes, six times per week. Reward yourself with a new warm up suit.