Petite usually means that they look like a loli but are older than they appear
All characters on Fakku are the "age of majority, notwithstanding suggestions otherwise", which means despite "appearing" or acting a certain way, they're all the age of majority (18). Fakku has been very careful not to license hentai that explicitly states a character's age for this very reason.
Which is probably the better option, in my opinion. I just wish they made this disclaimer more clear in the works themselves.