
no, they're in middle school. its literally in the story. all the boys are 15 which in china is the last grade of middle school. old xian's art style just makes them look older than they are. everyone gets shocked at first when finding out. this is why we get 'special' (usually holiday inspired) chapters of the couples in the future when they're adults. you'll know when it's the high school era because jian yi gets kidnapped on the 2nd day of high school (as said in the beginning of the story) and disappears for a while.

Omg it's good to know & yeah it's shounen ai, probably we won't see anything like yaoi, although maybe they decide to do some extras with their future self's, i mean why not probabilities...
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will they ever have sex?