I still say that whether or not a story is more juvenile, YA or adult, regardless of the "social age" of the protagonist, though, has to do with voice and tone of the work as well as the underlying "attitude" the author has about the situation the protagonist is in. I'd encourage you to read some YA books and some adult books with protagonists of the same approximate age as yours. This may help you get a sense of what some of the differences are.
This. In her culture she is a woman, and if you write her as such, she will be thought of as a woman.
And this. My ancient Egyptian character is 16. She's very self conscious about not being married, because it implies there is something wrong with her (actually her father failed to secure a husband for her because he was up to his eyeballs in debt and looking to turn her into a line of credit, but no one went for it)
And all the other girls are especially gobsmacked that she's still a virgin. Most of them lost theirs as 12 or 13.
One has to be a bit careful when assuming that girls in all ancient cultures (I don't know about Egypt in particular--I do know they married their royalty of both sexes off young for political reasons, but I don't know about the more common folks.
It seems to be a common misconception that girls in all pre-industrial societies were/are expected to become women and start having babies by the time they were 12 or 13 (typical ages of first menarche in modern, western societies). Even in modern America, where most girls hit puberty very early in historic terms, most girls are not terribly fertile at that age, nor are their pelvises usually fully developed for squeezing out babies.
Although it's varied in different times and places in history, the age of adolescence has actually
declined sharply in recent years. In the 1800's, for instance, it was more common for girls to start their menses around age 15, even 16. Girls in many pre-industrial cultures had/have later onsets of puberty as well. Historically, there was also a period of adolescent subfertility, which means that a girl was not necessarily fully fertile or developed physically as soon as she hit puberty. This period of sub fertility may be somewhat truncated in modern societies because of hypernutrition and a relatively sedentary lifestyle make kids accumulate body fat more quickly. But in a more historic setting, a girl who gets her first period at 14 may not be fully fertile until 17.
So while it is certainly true that the lag time between adolescence and the assumption of an adult role was diminished when compared to the postindustrial (where girls hit puberty much earlier and are expected to delay reproduction until well into their twenties at least), the notion that girls in all, or even most, pre industrial societies were being married off at 12 or 13 is not entirely accurate. The book
Mother Nature, by Sarah Blaffer Hrdy (1999) discusses this issue, actually, especially in chapter 8 (around page 186 in the hardcover edition I have). It's an interesting read, by the way.
I also suspect, though, that even in cultures where kids (especially girls) were expected to marry very early, there were still differences between them and older adults. There is a
fair amount of research that suggests that the pre frontal cortex of the brain is not mature until the mid twenties.
Presumably, though, your protagonist is not a "typical" member of your society, and she's being thrust into a highly atypical situation for her culture. If she is to make her way in the world, devoid of the normal social support network that young women/mothers in her society usually had (elders, mothers, aunties, grannies and so on), she
would have to grow up very fast or perish. She will likely have the traits that allow her to do this, or she won't survive or make for a very uplifting story
.