You can do it once a month or twice a day. The best rule of thumb is what makes your body feel good . If, however, you find you are always sore and in pain, you are most likely over doing it and should give your body more time to heal and rest between sessions. Yes, in fact, you are exactly who should be doing yoga. You just need to know where your limits are and have patience with yourself.
Some people are naturally more flexible whereas others require daily practice.
Also, yoga is much more than just flexibility . Yes, yoga is one of the best ways to reduce the stress in your life. Yoga teaches you to relax and focus within your practice. With a little time this discipline becomes a part of your everyday life. People will begin asking you how you remain so calm in such a stressful world.