You could be the President of the United States and he would not believe what is said. He already knows it all. The fact is you are a great resource for him, but not in his mind. Getting him past the “I know it all” is going to be tough.
My suggestion is to search youtube and other video places on line. Find some good videos that make some of the points you are trying to make, and a few other fun and cool videos. He can argue your points and disagree with you, but a video, they are fact to many 20 year olds today. I would use the videos as starting points to cover topics.
Some of the videos I have used in the past for those who know it all are here:
Link
Another video someone here on the forum found:
Link
I have found using videos as a good method to cover important topics and concepts. However, a few “cool” videos need to be sprinkled in to keep the attention.
If, the person is really hard headed I get a bit more abrasive. I tell them if they are willing to ignore or accept the risk to themselves that is fine. However, they need to get the okay from their mother, father, sister, brother, girlfriend, and so on that they will wipe his butt while he is in a cast healing after a crash. He needs to make sure he is not only willing to accept the pain, financial costs, but also the embarrassment of having a family members, friends, or a girlfriend wipe his butt and take care of the bandages after a crash.
For the most part, the abrasive approach has worked. The new rider may be bullet proof in their mind. But, as soon as I mention they may need to get their mother or girlfriend to wipe their butt for weeks or longer the attitude changes. I add to it by telling the new rider I am trying to keep them safe, but more then that I am trying to keep their loved ones from the heart break if something goes wrong.
I hope it helps.