On my right side, I felt a muscle cramping up. Immediately I stop what I'm doing when that happens. As slight and brief as the muscle cramp was, the area is still tender.
No matter what age, I believe, stretching is a component of keeping yourself healthy.
I learned in the late 1980s when taking martial arts instruction, stretching my muscles properly is as important as the action itself. Sitting on the floor in a leaning position with my head on the floor, I nearly fell asleep, I was that relaxed. The sensei explained to me to follow the right amount of stretching.
This morning is a wake up call. I am old. Stretching must be a daily routine. The odd moment of remember to stretch something isn't enough. A routine for all muscles at my ability level is the best way for me to keep healthy.