Just curious. I was 17 when I was last spanked. It was the day of my high school graduation. I held back my mother's arms and refused to allow her to beat spank me any more. I said I was too old and wasn't going to take it any more. She continued to struggle with me and I said if she doesn't stop I will strike her. She stopped. I said never again and walked away. One of my more shining moments. IRL I am only a few inches taller than my mother, but in my memory of that day I was like a foot taller, looking down on her as if I had superpowers.
Before that, I remember reading litter-ature to her that said you should use age-appropriate discipline, ie grounding older children who are no longer like younger kids (again who were likened to animals who couldn't comprehend anything but spanking). She responded by reading the scripture that says a child won't die if you beat him. I responded by pulling out newspaper articles of kids who died because of parental beatings. (Yes I kept them because I knew I was being abused.) She responded by reading the scripture that says not to question your parents or whatever, discussion over.
So what is the typical stop-beating age among JWs?