4 years old, don't be too strict, otherwise it will hurt his character growth. As long as you have a good grasp of the general direction, such as being polite to people, respecting adults, honoring elders and so on. This should be taught at ordinary times. Others should allow him to make mistakes and let him grow up with them. It is best to make him realize that some behavior is wrong, so that he can learn from it. Many times it is very important to set an example.