I started when I was 11 years old in 1981, with Moldvay Basic D&D. My next door neighbor Mark was the DM, running The Keep on the Borderlands in his basement for myself and two other neighborhood kids. We quickly acquired the AD&D books as well (DMG, PHB, MM), and mixed them in with the Basic rules. We thought everything with the D&D name on it was supposed to work together. And it pretty much did, more or less.