I am very jealous as I won't be anywhere near Amsterdam until I move to Europe in a couple years. It might be a little difficult for you to get weed (just as it's hard to get alcohol as a minor here, often even harder than illegal drugs) but I'm sure if you can get away from your folks you can ask someone over 18 to buy it for you. Try offering them a little money if you have to. Plan on getting 5 grams maximum as I believe that is the legal limit for personal possession, and beware people who might just take your money and disappear.