I had books later, when I could afford to buy a few. About 12 + I suppose. I earned pocket money mending things when I was old enough to bike to the library to look things up. Mother brought sewing machines from somewhere - they were mostly just out of sync. Electrical/electronic things had dud transistors and valves - OC83's and OC65's iirc. My father got old techy books from work friends I think. Several about old flying stuff. Aerodynamics of the Auster. Mechanics of car steering geometries, Ackermann and Davis. The importance of camber, castor and trail, and then motorbike suspension. Still have meccano in the loft.
I was given an Intel 4004 processor when I was about 15-16 so I had loads of datasheets on its primitive assembler and circuits. I read those under the bed covers
. Then 6800, 8080, 6502, Z80,...
And stuff from National Semiconductor - their linear circuit applications books were informative. 741's and 555's were new then, I couldn't afford those until later.
I had an early poorly illustrated book on cryptogams, and another on bugs.
Thats mossy things and blood/sapsuckers (hemipterans), not computer related.
Still have a head full of names like rhytidiadelphus squarrosus, amblistegium serpens and palomina prasina.
Also got hold of a mathsy book on Laplace transforms, Heaviside and Delta-Dirac functions which I learned because I liked the way they looked and fit each other. There's no point learning them, you just look them up, and I don't remember using them much, ever. I wish I could forget them and have that bit of brain back.
I refused to learn kings and queens because they're dead and didn't matter any more. Now I could learn them but would forget them in a week.
I had a green Collins dictionary, which annoyed me because I couldn't learn it. But the inside covers had all sorts of learnable stuff on them, like the Greek alphabet and German strong verbs. Remember those? I learned em though I didn't know any German then. Broken Welsh coal averages one ton to 40 cubic feet. Pi and e to 20 places, etc. The Periodic table, natch. They went and changed it later, b'stards.
Oh and times tables up to 20x 20. Handy for Countdown.