I don’t use drugs nor alcohol, but I just turned 18 and I noticed that a lot of people younger than me (high school age so 14-17 even) use alcohol and sometimes drugs from siblings, older friends, etc.
Did you do that when you were younger than me? I don’t plan on doing so anyway.
In the UK it’s quite common for kids at some 15/16 to have house parties with alcohol (our drinking age is 18). At least this was common when I was that age 16 years ago