The shoulder is one of the most complex joints of your body. You use it all your life in a variety of positions. But with age its mobility gets compromised. So what was a normal movement can become impossible or painful.
This exercise and its progressions can help you regain or keep mobility. All you need is a band or a belt, a rolled towel or a elastic band.
Warning: Level 3 of this video is not to be attempted before being comfortable with level 1 and 2. And is not to me attempted if you have any medical contraindication.
If you need a regression to L1, you can also lay down and do it against the ground. Gravity will help you stretch and it will feel easier.