About their ages?

Background: So I watched this show from season one to four on repeat when I was a younger but didn’t know they were still making episodes until more recently so I decided I’d rewatch the show (I hide the fact I watch this as if I killed someone as I watched this when I was like 10 or 11 and I’m 15 now😭)

The main thing: I’ve looked up how old the characters are supposed to be a few times and it’s said that in the first season they’re around 13 or 14 but in “The Pharaoh“ it’s suggested that they’re in high school, specifically 10th grade I looked up stuff about France’s schools because I knew they were different but it kept telling me France’s 10th grade was equivalent to America’s so idek can someone help me out here😭🙏