Why tf do people look older then they are

It's fucking crazy how kids who are 14 look fucking 20. Like a few weeks ago i was at a shisha bar w some friends and this girl who knew my friends comes up to say hi and she was likw how old r u and i said oh im 17 wbu and she was like 13. WTF. Like nobody looks their fucking age, then u get 17 year old looking 12.