Again, age them up because everyone is just going to keep question it because normies and outsiders aren't Sonicfags/children. You're never going to justify it just because everything else these characters do mimic adultry stuff.
It's like saying Jimmy Newtron isn't 10 just because he flies space stations and creates time machines. When he was shipped with Cindy it was cute at first but when they wanted it to go deeper they aged up the characters by the end of the series to almost teenager ages.
Fiona will always be the most awkward stage in Sonic media that people will laugh at when said without context because Tails being 8 is far more well known than not.