My father smoked marijuana in front of me in 1971. HE might have been an adult before he heard of it, but not me.
What time frame are you talking about?
My brother graduated from HS in 65 (he’s 7 years older than me). He says pot was just starting to show up in our smaller Midwestern town when he was in HS.
The 1910s/20s for my grandparents, and the 1940s/50s for my parents. They never even heard of “marijuana” until they reached their adult years, and it was likely from a magazine article at that.
Much later, I went through my entire high school years and college years without ever seeing a single person smoke a marijuana cigarette. Not the kind of crowd I’d hang out with.