It doesn't make a difference unless you let it make a difference. Some people in my highschool let drugs fuck them up pretty bad. Other people were even more responsible than I was and didn't let it effect them at all. I think the biggest downside for drug use at a young age is tendency for young drug users to also (in general) be not the best people to hang out with. The most responsible people, who use drugs imo, tend to start when they are freshmen in college or seniors in highschool. I really think people who start younger are statistically more likely to become involved with other criminal activity, but I really can't say it is just my own little perception of a tiny subset of a tiny part of the world . And of course correlation and causation....I actually blame prohibition for a lot of these problems.