Use a broom stick, staff, or paddle.
Start with a wide grip, thumbs facing forward.
Bring the staff down behind your head, between your shoulder blades as far as comfortable.
Next take the staff back, straight out away from your body.
I also learned this one from the guys at GMB (Gold Medal Bodies)
As we age, training to increase/regain joint mobility becomes even more important than building strength.
Mobility is part of correcting posture, which makes all our movements lighter. Not to mention our moods :)