NTA I'm pretty sure you are in England and as far as I know legal age to drink or smoke is 18, which is the same in my country. You are lucky that your kid, who is days away from being legally an adult, came to you to talk about these issues. Sadly for many kids it is usually their friends that introduce them to these addictive substances, with a bit of peer preasure involved and sometimes in situations where they can be vulnerable. I understand the reasons behind what you did and can only find fault in your method if there was no linformation given about the many dangers of alcohol and cigarette addiction. I grew up in a country where 18 is the legal age and due to skipping grades I started college at 16 so my parents sat me down to talk to me about smoking and drinking since most of my classmates would be old enough to do it legally. My Mom did neither but my Dad did both so I got different perspectives and I was asked to come to them if I ever felt curious or pressured to do either. Well eventually I did and I was allowed to try them at home with my family and I realized that smoking was disgusting and that alcohol can go to your head fast. So after that it was easy to say no when I was offered either by friends. I'm in my 40s and I don't smoke and I drink only on special occasions and very little. My brother also in his 40s, who got the same talk and tried at home with Dad, drinks and smokes but only when he is socializing. My son and his daughter are both over 18 and they received the same talk and chance to try at home, they don't smoke and drink very little mostly on special occasions.