1979, I was 11 years old. My older foster brother had been acting kind of sneaky for a few weeks, and it turned out he had been learning about D&D from a schoolmate. He avoided introducing me to it for some time, as he was concerned that our parents (my dad in particular, a minister) would disapprove (turns out my dad was fine with it, though his views on D&D and other topics would come back to haunt him much later). At some point, though, he discovered that he had a captive audience in me and started me off in module B1, In Search of the Unknown, which I believe he failed to stock with monsters.