I cannot remember any clear-cut stages in my developing as a reader, in the sense of progressing from one kind of book toward another; it all went parallel. Between ten and twelve I read tons of adventure stories of all kinds: Walter Scott, R. L. Stevenson, Jules Verne, Jack London, H. Rider Haggard, Thomas Mayne Reid, Fenimore Cooper, Alexander Dumas.
While the other books were very much my private reading, adventure stories were always shared. Someone in school would start reading and suddenly everybody was talking Leatherstocking or D'Artagnan, and unless you jumped quickly on board you were left behind. Most adventure stories have male protagonists, but I didn't mind, and if there was some romance on top of adventure, it was a bonus. I had two particular favourites, possibly because of the prominent romance: The Quadroon and Montezuma's Daughter. Robinson Crusoe I found boring. Much of the attraction of adventure for me was the historical background. I liked history in school, and we had a wondeful history teacher who made it a very vivid subject, but I think that until these days most of what I know about history comes from novels. Which also accounts for huge gaps in my historical knowledge if no novel has ever described a historical period. Fortunately, all interesting historical periods have been treated in novels, but the truth of that knowledge can be rightfully questioned.
With my passion for astronomy, I read a lot of space science fiction, but I also liked earth-bound science fiction about lost worlds, underwater worlds, undiscovered continents, forgotten civilisations, hollow earth, tropics at the poles. These were enticing because they contained a promise: there were still things to be discovered. Space travel, on the other hand, felt just around the corner, and although we knew that one could not travel to the Moon in a cannon ball, space ships were already a reality. In fact, I was absolutely sure at the age of ten that I would within my lifetime be able to travel to the Moon, Mars, Saturn and beyond. (My persistent motion sickness didn't pose a problem).