Cars. I had a huge collection of Hot Wheels and Matchbox cars, and obsessed about being able to drive a car.
Trains. I had several toy/model train sets, and loved watching trains at crossings.
The space program. An early memory of mine is watching the Apollo 11 landing, at age 4, and I loved reading about space exploration. By the time I was 10 or 11 (just before the OP’s age cutoff), that branched into model rocketry.
Weather. I was a weather nerd, and by age 5 or 6, had decided I wanted to be a television meteorologist.
When I was about ten I got a chemistry set. Back in the day, before liability became an issue, chem sets had real chemicals in the them, some dangerous. I did all the experiments in the manual and then devised some on my own. I had a real lab set up in the basement and was convinced that this was what I really wanted to do in life. When I got a job in an actual lab at age 17, I discovered I wasn’t very good at it.
Playing cowboys and bad guys. There were tons of movie cowboy heroes in the 50s, and we all emulated them. A lot of the toy six-guns were very realistic-looking, and this was way before the bad times we have now with firearms. I was also obsessed with reading, which continued throughout my formative years.
The first but not the last. My obsessions were horses, drawing horses, watching horses, reading about horses, talking about horses, and also, horses. I read every single book in the public library about horses. When I was eleven I finally was given a decrepit ancient gelding, and became part of a gang of horse girls (who all had a horse of some kind). When we couldn’t ride our real horses we held horse shows in my living room, including Open Jumping (sofa cushions), and even calf roping using our cat Armpit as the calf. This lasted through two entries, after which we couldn’t find him again.
Stats. Especially baseball stats. One of my earliest memories is the Maris/Mantle home run chase in 1961. I lived for the sports report on the late news.
I was fascinated by chess aged 5 (after I saw it on ‘Blue Peter’*.)
My parents didn’t know how to play, but bought me a pocket chess set and got the book ‘Chess for Children’ out of the local library.
I taught myself chess and practised on my own turning the board around between moves and reading more Library books.)
When I was 13, I joined a local chess club (and discovered I was jolly good. )
Since then I’ve played chess in many countries, won various titles and even had a fantastic job teaching chess full-time in a UK private school.
Boats. I found a model boat at the old family farmhouse barn and became obsessed with making it work. This was just a carved wooden thing. I built it a mast and a new keel and finally got it to where a breeze would make it go.
In the years since I have had…not good experiences on boats. The only thing I’ll go on now is a party barge or a car ferry.
I’m the third! I loved, loved, loved horses. (I still do.) I never had one, but I sure dreamed about having one. I read every book ever written about horses (I still have them!). I would pretend our lab mix dog was a horse. I would brush him and set up jumps for him. I bought a harness for him, because it was more horse-like than a collar. I had it hanging on a nail and would pretend I was tacking him up for a ride. I loved dogs and other animals too. But horses were number 1 on my list.
I also loved to read. I was always reading.
And David Cassidy, he was my crush for a few years. I still enjoy watching the Partridge Family!
The World Book Encyclopedia and its companion Childcraft
The Choose Your Own Adventure series and Which Way Books
The Guinness Book of World Records
When I was 10 I got a copy of Reader’s Digest Mysteries of the Unexplained which started mi interest in paranormal/supernatural stuff leading me to get books on the subject by Brad Steiger, Charles berlitz and Daniel J Cohen
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