Kids cartoons have cute and young characters. Especially women because they are more attractive when they are young. The WW on your picture doesn't look older than her late twenties and she probably never will in any popular media. The only thing make her look older is the thicker figure which is usually associated with more mature women, compared to the skinny teens. This TTG WW seems like she is a teen (which is actually hard to say because every characters design leans towards young and cute) but only because the other girls look much younger in the show.
Princesses (girls) get all the action in every media and queens (women) sit at home being boring. When you look at older and younger heroines (not the youngest) there are 5 years between them at max. Older is just making their figure fuller, their body taller and giving them a serious face. If they want to go older but not too old, they usually do it with clothing and heavy makeup maybe some wrinkles below the eyes. Queen Hippolyta replaced Diana several times in Wonder Woman comics when D was missing because as soon she dropped the toga and put up the bikini armor she was almost indistinguishable from her daughter.