Enroll for a course in yoga, if you have not done one earlier. With each stretch, it gently aligns your body's muscular, skeletal and nervous systems. It relieves pains, corrects postural problems, massages internal organs and stimulates the endocrine system. It reverses the effects of aging.
Hatha Yoga is one of the most sustainable form of exercise after walking. You can do it until your dying day.
Just 15-20 minutes every day can make a world of difference to your energy levels. To ensure motivation, ensure you have a group of friends and family with you, so that you can look forward to doing yoga every day.
Related: Surya Namaskar