This is the real answer. Really, really gross, just not necessarily illegal.
Age of consent varies. Example in Victoria Australia is it's within 2 years until 16, anyone from 16 as long as they're not your teacher or someone else with authority, and then 18 anyone older than 16.
Prevents stupid shit like I've heard from the US where an 18 year old gets booked because the parents don't like that their 17 year old is having sex...
Don't look up the age of consent in China, they've really dropped the ball on that one 👀