Anyone can learn Yoga and benefit from it. Yoga is not just for those who are strong, flexible, thin, etc. Yoga is a discipline open to everyone and it gives us the opportunity to come to our practice as we are: working within our own limitations, strengths and weaknesses.
We just need to approach the practices with an attitude of openness and self-acceptance.
Even though we do work with the body, through postures and movement, and there are undeniable physical benefits deriving from the asana practice (postures), getting fit is not the ultimate aim of the practice. Even the physical practices of Yoga are a tool through which we can find more ease in our body and create harmony between body mind and spirit and become aware of and, eventually, experience the ultimate nature of existence.