The problem is rarely the uniform but the body underneath.
Loads of posts on here where a pair of trousers that is fine on one girl is deemed "distracting" or "unsuitable" on another who has a more adult figure.
Same in this case.
Girls at secondary school are growing into women of course some will have bodies that look more adult.
The problem is that female curves - waist / bust / bum > are coded as SEX in most (all?) Western societies and normal girls bodies themselves are deemed scandalous in some way. And the the girl is shamed / punished.
The issue is with men and the fact that many of them see curves and think "sex" and also "old enough" and then say WAAAH I thought she was younger. NO. Girls who are past puberty and growing have ALWAYS LOOKED LIKE THIS and men have always said "I thougth she was older". What they mean is that if girls want to stay unsexulaised and unogled then they should look like girls not women. Of course this is impossible.
Society needs to adjust it's expectations of what girls of different ages look like to meet reality and then treat children as children, and womens' natural bodies need to stop being simply shorthand for "sex" and somehow obscene.
Is my view.