Why would you start practicing Yoga? Why would you start especially if you don't feel flexible, mobile at all? Coz' Yoga is not about flexibility. Yoga is about connecting with yourself, exploring body and mind simultaneously. Getting to know yourself slightly better, never for the worse or the better, just for the sake of knowing who you are.
This is why we are, what we can keep doing throughout our life, even without a super duper Yoga mat, bricks blocks and straps. Even sitting on a chair, with eyes open or shut, with hands in a mudra (hand gesture) or laying or your lap. Just being and finding comfort in just being, not having to do something in particular, not having to say you are doing it, not having a selfie of yourself doing it. Because at the end nobody else cares. But you care about yourself and this is essential. This is life.