>>90755643Star definitely isn't an expert, but we can draw a few conclusions from the evidence we have.
The Mewberty/Butterfly form is definitely connected to their magic. Both of the times we've seen Moon use serious magic, she's Dipped Down and assumed her Butterfly form.
The Butterfly family's cheek emblems are also related to their magic. But of all the Butterflys we've seen so far, only women have had cheek emblems.
This suggests that the root of the male/female dimorphism in Mewmans lies in their magical ability, with Mewman girls being significantly more magical than Mewman boys, and that the royal Butterfly bloodline in particular is exceptionally gifted in magic.
Mewberty as we understand it is a female thing, and considering the only physical change it causes is the growth of immature wings, it's probably more of a magical maturation than a physical one.
This also explains the Butterfly Kingdom's matriarchal society. Part of it is rooted in their biology, if adolescent Mewman girls go through some magical metamorphosis and essentially try to start a hive with available mates. But the Johansens are also Mewman and there's no indication they are matriarchal. More significant is the Wand that the Butterfly family used to carve their Kingdom from the savage monsters, an unstoppable force with the might of their Queen's magic behind it.