Look at the Princess' description in the game, they wouldn't talk about "having warm feelings" towards her if she was underaged because that would be creepy. Also in the clash a rama series you see that the Prince and Princess both like each other, and the Prince is an adult himself, and the Knight (who's also an adult) I believe liked the Princess too and the Executioner clone (who is a middle aged man) and Archer also like each other in a different episode, so she likely isn't a minor too. They wouldn't showcase grown adults dating minors in a show without them getting in major trouble. Plus if you click on the Archers profile too she also doesn't look like she's under 18 and I don't think they would draw her like that if she was. It's just young and dumb kids who think that because they look "small", they're automatically underaged when that's not case. The Rascal boy is large but is assumed to be under 18 because of the use of the word "boy" and is the older sibling to the Rascal "girls".