Your child is now going to school and would be interacting with people of his age. He would be encountering teachers as well. This is the correct age when you need to make him realize about basic habits that makes him a humble person. Your child may catch negative behavior traits, teach him to take permission on different occasions.
What you need to know:
At this age, the concept of taking permission must be new to your child. So, he may take some time before getting rightly into this habit. Be patient and allow your child to learn it in his own time. You can make him practice taking permission while going to the washroom, picking up something from your room etc. This is a good habit which should be taught to your child. Ask him to practice this at school. Not only with elders but this act should be implemented when taking something from fellow students. Make him understand that taking permission also means that he is valuing other people things. So, you as a parent should also practice this behavior so that he can learn through you as an example.