“Old man, stiff man, weak man, sick man, they can all take practice but only a lazy man can’t take practice.” Sri K Pattabhi Jois
There was an inquiry on the APP regarding Ashtanga and being overweight. Anyone can practice Ashtanga. Ashtanga is best learned using the Mysore style method which is learning the practice pose by pose from a teacher who has a firm and consistent practice. When learned this way, the teacher will teach you how to approximate ie get as close to the full version of the pose as safely as possible.
The key here is finding a teacher who understands your body and knows how to work with it. I do not recommend trying to use a book, videos, or the internet. You need someone working with you pose by pose to keep you safe. I also do not recommend dropping into a guided Ashtanga class. It is too fast. The point of a traditional guided Ashtanga class is to the keep the count and stick to the prescribed vinyasas. The teacher will not have time to work with you and keep each pose to 5 breaths each. Mysore style Ashtanga teachers can work with you on each and every pose.