When I was 10 years old (1986) somebody bought my friend the red Mentzer Basic Rules boxed set. We passed the Player's Manual around over the course of a week or so among a circle of I think four friends, and each of us played through the starting solo adventure. I thought it was amazing.
Within a week we had a basic understanding of how to play. We started running the starter adventure but found it too deadly and could never get very far. We had more success running our own (very simple) adventures. About a year later we moved on to AD&D, and then a year after that 2E was published and we switched over to that. The adventures became gradually more sophisticated as we got older. We almost always homebrewed the adventures because anytime we tried an officially published one we found it pretty horrible (I think the 5E ones are much better than any 80s adventures).
Looking back, what surprised me is that we (more or less) played the game "correctly" despite being self-taught and having never seen the game played or had anyone's older sibling to teach us.
It was years before I met anybody outside my circle of friends who played.
Our last major campaign was in 2E, starting in 8th grade (on April 2, 1990) and continued through our graduation from high school in spring 1994. I then didn't play again until 2017, barring a couple of abortive attempts to play 3E in my early 20s.