I looked it up and according to the Web Novel she's 17, so we were both close but wrong^^
And most of your observation aren't really a sign of age, Maomao was born and raised in the Red Light District and was the apprentice of a (suspiciously) talented doctor. More than a sign of age, her reaction and logic stems from growing up in a harsh environment. It will be explained later, but it's also worth noting that Maomao is basically a genius, explaining why she is so knowledgeable and mature despite her young age.
And the definition of women depends on the era, in the middle ages, you were considered marriageable as soon as 13-14 depending on the necessities.