I congratulate you on your decision to take up schedule of yoga. You need to consider the initial position and final positions of asanas you attempt. You have to listen to your body where it alarms you and warns you not to go beyond that point. Just try to go for final position not accurately but effortfully. This will give you full benefits same as taken by yoga practitioner who is doing for long years and perfectly since it is the matter of stretch and relaxation of muscles. So, start from today itself without any fear. You just need to learn to listen to your body. If your body alarms with pain, do not go beyond that point as it indicates that either you are over exerting or wrongly attempting.
All the best !
One thing more, before yogasanas, always do some warm up and after yogasanas, always do relaxation with deep relaxation technique or yoga nidra. Focus on your diet as it will help you increase flexibility as well as gain the benefits of yoga schedule.
Once again all the best....
Another thing to be remembered to learn from some qualified yoga practitioner. He will be able to tell you limits of your body as well.