You can start corporal punishment as soon as you know that the child understands basic terms like "No!", "Don't", "Bad", "Good","Not yours", "Quiet!", "SHHHHH".
This way, you know they understand enough to make decisions, and follow rules and commands, and have some idea what the command means.
You could start earlier than that, but it will not work as well; it would be more like training a pet for lack of the stated qualities.