Also her mom is ditto like mine.

I think the school system is different from the U.S. She would be a freshman, 9th grade, but I'm pretty sure it's considered middle school (6-9 or 7-9 I think, idk). I was 15 when I was in 9th grade, so I think her age is normal. But she'll be 15 or 16 in 11th grade because she's probably gonna skip 10th. Hope that helps some.

Tbh I dunno what language the work was originally in, so I can't guess, but if it's either Chinese(manhua), korean(manhwa), or japanese(manga) or some other because as far as I know all three of these countries have different age systems than the international counterparts. Japan and Korea both assign the child to be 1 year old at birth and you only turn a certain age at the new year instead of your birthday and in chinese you can be 1 sometimes 2 years older than your international age. I'm inclined to believe this is a Chinese manhua because of the names and a little because of the art but I still don't know for sure.

its a manhua

It’s a Chinese Manhua. I’m pretty sure they are using the international or “normal” way of counting one’s age instead of the traditional Chinese way. In Korea, Japan, and China, middle school is from grade 7-9 while high school is from 10-12. Since she finished the 9th grade or 3rd year of middle school at the age of 15 and immediately took the exams for the 10th grade, she might skip a grade and immediately be an 11th grader

ye and they also use "Mèimei" and "Gege" which in china it means younger sister and big brother correct me if im wrong

Yes. I’m actually part Taiwanese and this is what we use to address some family members. “Mèimei” means younger sister, “Dìdì” means younger brother, “Jiějiě” means older sister, and “Gēgē” means older brother. And this is in Chinese Mandarin

The school years are divided into:
6 years of elementary school (6-12),
3 years of middle school (13-15) and
3 years of high school (16-18).