Here is Bernice Bates, 91 years old and teaching yoga at her senior center to 60 - 80-year-olds! She has been practicing and teaching since 1960. I love this quote from her:
"Yoga itself means yoke, that's to join. We join our mind, our body and our spirit in everything we do. Yoga gives you flexibility like you've never had before, and it makes you healthy because you're working on the whole body, inside and out."
Yoga studios are everywhere, local gyms usually offer yoga classes, and there are hundreds of good books about yoga. You can even find apps for your smartphone to help you with your yoga practice. I like the book Yoga as Medicine by Timothy McCall, M.D. As a medical doctor, Dr McCall sees (and uses) yoga as therapy, a "yogic prescription for health and healing." For runners, I recommend The Runner's Yoga Book by Jean Couch. Jane gave me a handy little yoga book to take with me when I travel, The Athlete's Pocket Guide to Yoga: 50 Routines for Flexibility, Balance, and Focus.
You can get the books at Amazon.com: