I have a question, two of my main characters in my novel are twin sisters who are twenty-one years old, while their younger sisters are Eighteen and Sixteen in the current draft that I'm writing.

All four sisters play a major role in the overall storyline. The only thing that I'm curious about is if the ages of my characters is too high. Most YA that I've seen tends to have younger characters. The twins used to be younger in older drafts, and I gradually changed their age as the storyline changed.

Are the twins too old to be the MC's in a YA novel? The genre is Fantasy if that helps.