Pretty sure I have written about this on this forum once or twice already...
Started playing wargames in 1972. mostly with the 1/72 scale Airfix and Caesar minis. Was an army brat, and found the minis in a German toy store in Frankfurt. Had a great collection of WWII minis by the spring of 1974 when I moved to South Carolina. There my Dad made friends with a guy who was in Army Intelligence, and he wargame heavily using the old SPI and Avalon Hill board wargames, and he got my Dad to play, but my Dad didn't really like playing. I watched, and I liked playing though, so he gave me several wargames, I remember SPI's Korea, and Huertgen Forest, and Aa couple of the ancients Quad games. For my Birthday in 1974, my Dad got me a copy of Panzer Leader. WIth the open random scenario design built-in for replayability, that was the game that got me hooked on wargames. I could recreate any WWII European land battle on a regiimental or brigade scale, using just that game, and spent hours playing with my Dad's friend. When I moved to Colorado in February of 1977 I had a pretty good selection of more than a dozen wargames, along with my 1/72 collection.
I was in junior High School at the time, and met some new friends that also wargamed. And I remember that Squad leader had just been released, and I had mail ordered a copy, and called my friends over to play. Turns out one of my middle school friends had a neighbor in college, by the name of Doug who wargamed too, and he was back from CSU ROTC on Holiday and looking to play some games. He had bought a D&D 74 brown box at Origins in the summer of 76, and right after Christmas had showed up wanting to play with us, because none of his college friiends were around, so we played D&D for the first time, and I died alot. I really liked wargames, but this was just as good!!!
So I started saving up to get my own books. By May of 77, I had a Holmes Bluebox, and a copy of the Judges Guild Ready Ref Sheets, and was running games for my middle school friends. We mixed it up a lot. One weekend playing D&D, another playing Squad Leader, Panzerleader, or Alexander the Great, or Submarine, or Bastogne, or Wooden Ships & Iron Men. As the 70's turned into the 80's we met more gamers, and started playing using minis, like 1/285 Tractics, I still had my 1/72 collection but no one but me and a couple of my High School friends ran games using those. Mostly we would find a place outdoors to play, but I had a huge basement with shag carpets and a HO model railroad, and played WWII games on the railroad table often. By 78-79 we were playing Boot Hill and Gamma World,and I had picked up Traveller in the winter of 77, I remember making new subsectors when it was snowing outside and really enjoying snow days from school so I could work on my Traveller game all day long.
In 79 I went to my first gaming convention. Ghengis Con I in Denver, and we (being me and my high school gaming group) mostly played in State Wargame championship tournaments. We also bought RPG books, and brought them back with us. In 1980 RPGs really took off in Colorado. Greg Stafford was at Ghengis Con, and he had just published a new edition of Runequest, which I tried at the show, and didn't like, because I wanted to play a human, and everyone else wanted to play intelligent critters. While we had four hundred or so players in 1979, there were over a thousand gamers that showed there in 1980. I started trying other RPGs besides D&D. Arduin, The Fantasy Trip, which I liked alot, Tunnels and Trolls, which never caught on with me, Warlock, the Caltech D&D variant which I liked very much, and continue to like even now.
I still played wargames, However played D&D or Gamma World or Traveller, or a mashuip of these three games just about every week. By the time I had graduated from high school and joined the military/entered college, I had a wargame & RPG collection that was worth much more than my car.
It was all pretty relaxed and we had lots of fun. I didn't really get on the AD&D train, finding D&D was quite sufficient for everything I wanted to do as a GM, although I did play AD&D and rolled up advanced characters when my friends GM'ed AD&D in the late 70's and early 80's. I used the monsters out of the AD&D Monster manual for my whitebox D&D games, and used random generation tables from the back of the AD&D DMG, to help me make a better D&D game, but never fully adopted AD&D as my primary RPG game. It was all mostly interchangeable, well until 1980 anyway.
In 1980 newly founded RPGA would not let me run D&D games at Ghenghis Con and insisted I run AD&D games. I ran D&D anyway, the way I wanted, but wasn't listed in the prereg book, and was very unhappy about that.