Is there an age when you begin to spank? And at what age do you stop?
There is no excuse for spanking babies or children younger than fifteen to eighteen months of age. Even shaking an infant can cause brain damage and death at this delicate age! But midway through the second year (eighteen months), a boy or girl becomes capable of knowing what you're telling them to do or not do. They can then very gently be held responsible for how they behave. Suppose a child is reaching for an electric socket or something that will hurt him. You say, "No!" but he just looks at you and continues reaching toward it. You can see the smile of challenge on his face as he thinks, "I'm going to do it anyway!" I'd encourage you to thump his fingers just enough to sting. A small amount of pain goes a long way at that age and begins to introduce children to realities of the world and the importance of listening to what you say.
There is no magical time at the end of childhood when spanking becomes ineffective, because children vary so much emotionally and developmentally. But as a general guideline, I would suggest that most corporal punishment be finished prior to the first grade (six years old). It should taper off from there and stop when the child is between the ages of ten and twelve.