1992
That's "for real" D&D. I got into Endless Quest books after I read all the Choose Your Own Adventure books out at the time. I knew that they were connected to "Dungeons and Dragons", which (as I understood it) was something involving spells, and divinations, and horrible, nameless creatures that moved in the dark (all of which sounded awesome), and (as I was led to believe) included a crystal ball, a skull, and a dagger, all in a giant $200 boxed set that you could only mail order direct from the manufacturer. (Ahh, the eighties, when the hover board was eternally "coming out next year.")
Anyway, I went to scout camp in the summer of '91, and got introduced to something that greatly resembled Dungeons & Dragons, only it didn't, except for the name, and there were orcs. There were no books, task resolution was handled with playing cards, and dwarves (such as myself) could wield highly destructive magic. (Which, they then, of course, couldn't, and which I did, with great relish.) As I recall, we battled tribes of orcs (which were at war which other tribes of orcs (which we had enslaved (and lived in huge castles (which were contained inside a bag of holding that we carried around)))) with magic dynamite, and big swords. And "magic missile", as far as I could tell, was essentially a Stinger that trailed fairy dust. It was AWESOME.
Flash forward a year later, and I finally managed to get copies of the 2e PHB and DMG, and (a short while later) the Forgotten Realms grey box set. I can't even tell you how many times I herded groups of green adventurers through the two mini-dungeons that came in the FR box; I never got tired of it.
Fifteen years later (yikes!), I still haven't.