I could read well from a very young age. The local library wouldn’t allow children in the main section, so I searched the children’s level until I found some science and science fiction books because they had the most advanced vocabulary, etc.
‘Starship Troopers’ was one of the first acceptable books I found there and I was hooked on science and SF! About age seven.
I was reading at about seven as well. My first SF book was "The Star Conquerors" by Ben Bova (1959), shortly followed by "Raiders from the Rings" by Alan E. Nourse (1962). I was continually signing them out of the library.
When the library was getting rid of its older books, I made sure that I purchased both of these for my shelves. I still have them ...
Weird!
I had the same problem with our Catholic school library (it was Grade 1-High School at the time, Christian Brothers).
At age 6 they would not let me into the “big boys” section. I bitched until they did.
“Starship Troopers” also. “Moon is a Harsh Mistress”
A bit later, “Glory Road” . I found it as a adult though.