Maintaining good shoulder mobility throughout life can easily be worked into a task that we already do, reaching behind us to wash our back.
As the years progress, you might not notice that your shoulders are becoming more tight. Yet it can happen because you might not be using your shoulders to full capacity to reach up, across, or behind you that much. These are all motions that get used when you wash your back in the shower. Even if you use a shower brush, it will still be helpful.