Well I did it when I was in elementary school. I think I started in 3rd or 4th grade when my parents started to realize that it was a problem for me. I did it up until 5th grade and then my parents thought it was no longer a problem because I was a good talker at home. I don’t really know exactly how long you should keep him in, but I would recommend you keep him in until the end of elementary school then ask him if it’s something he would like to keep doing. He’s 7 so I think at that age consistent speech therapy would be great for him so that he doesn’t develop bad habits.