I was 29 before I took any kind of drug. My best friend who I've known since 10 has been doing a variety or drugs since he was 19-20 and I had no idea until 11 years later. He always tried to keep me shielded from it, and I appreciate it so much, otherwise I'd have been burnt out by 20 with mental health issues.
18... I mean wow I'd have ruined myself, I was an immature dick at 18. In fact I was an immature dick right up to about 22.