You will obviously do what you feel you need to do as a parent but I wouldn't worry about pot as a danger. Maybe try and educate him on it and some of the negative health implications (which aren't many). I started smoking cigarettes around 12 years old and pot around 15. The biggest problem I've ever had with it was with my parents. Eventually you grow out of it and learn to use responsibly but it would have been better if my parents had taught me that from the start. The same goes for alcohol. I used to get completely drunk all the time but probably wouldn't have if I didn't have to sneak around behind my parents back.