Maybe not of the same era but I read a lot of 1930s-onwards horse-related stories where female protagonists had a lot of freedom, adventure and there was an emphasis on self-reliance, responsiblity and 'good character'. Similarly with all those boarding-school stories. Similarly Swallows and Amazons, in which the characters were teenagers. We may misunderstand them as younger because they were viewed as 'children' at a time when teens didn't exist but they have enormous freedom and self-determination.
I read all these from 7-11 but that's also true for Katy and Anne (which was read to me when about 6, along with the strong and adventurous Little House on the Prairie series), so perhaps definitions of 'teenage' books depend on the reader.
I think readers identify with the protagonist of whatever they're reading, whatever their sex, and often chose books for type rather than characters, initially. That's why no-one identifies with soppy Anne in the Famous Five - if you were that sort of girl you wouldn't choose to read those books.
By reading to themes e.g. horses, I stumbled across a surprising range of books and styles I mightn't have otherwise. The 'My Friend Flicka' trilogy was a real surprise. These are deeply humane and insightful stories about family relationships, differences, loneliness and fulfillment. The sensitive younger son, who doesn't meet his father's sporty and military aspirations, finds solace in horses and is a sympathetic protagonist for readers of either sex. Unusually for a children's book, there is some focus on the parents' perspectives, particularly the mother and her isolation, living mid-nowhere in a male household and, on her husband's awareness of this. There is also some powerful horse on horse violence, which mirrors the human generational power-stuggle or perhaps an oedipal theme. Not a 'fluffy little girls' book about ponies' at all.