They're 17 iirc
17 in korean age most likely so they are around 14-15 international age.
I went to check and I don't think the author applied Korean/Int system, she wrote in their character profiles 17 for Ian and Yugun, and 18 for the seniors without adding anything.
Yes bc it is mostly implied in Korean works. But the government has now chosen to legally abolish the practice so they may start mentioning or something.
Are the main couple like 15/16? because I seriously can’t tell how old they are but they def under 18