THEY NEVER GAVE A SPECIFIC AGE TO PAPI OUSTSIDE OF HER BEING THE SAME AGE AS MIIA, WHO IS OF LEGAL AGE OF CONSENT. ALSO, IF YOU READ THE MANGA PAST WHERE THE ANIME STOPED, YOU'LL LEARN THAT *POSSIBLE SPOILER* PAPI'S MOTHER IS PRETTY MUCH AN EXACT CLONE OF HER (WELL... HER WITHOUT MAKEUP AND HAIR DYE) SO WE DON'T NEED YOU JUST YET, MR. HANSEN!
You expect a something that flies to stand at five foot seven, have larger than A or small B cups, and have the body mass of an adult female human?
Papi's aerodynamics are pretty screwed already, the explanation given for her appearance is logical. Being really forgetful and high energy probably doesn't help.