Anyone can do yoga!
One of the beliefs that keeps people from trying yoga is that they have to be in shape or flexible to start the practice. Not true, it is called practice for a reason. I have seen people who started their yoga practice with a chair and if they can do it then you can too. Yoga is a mental and physical practice and can also be a spiritual practice as well. If you want to improve your current situation, yoga can help you achieve your goals.
To keep yoga safe for everyone yoga teachers will always give safe alternatives to every pose so that everyone can enjoy their time in self improvement. It is always acceptable to just sit comfortably and breathe deeply. That alone can have major health benefits like lowering your heart rate and reducing your adrenal stress. Breathing correctly is hard work and can strengthen your core muscles. Have fun learning to breathe with locks a term that is all about active diaphragm breathing.
I look forward to the day when community out-reach programs and churches are involved in yoga or stretching activity classes helping all ages including seniors and even shut-ins. They will breathe, stretch and have health improving activities that will maximize well being and reduce health care (sick care) costs one healthy person at a time. These programs will spread throughout these United States of America. So until then, keep doing the best you can by spending an hour, a half hour or even 15 minutes a day improving the body you live in.