Do breasts have to sag?

[James]

Wait wait wait! I can hear the groans all over estrogen dominated GC that this is another sex post . . . but its actually a genuine question.

Why do some women regardless of the size of their breasts or their age sag, and others regardless of size or age stay perky?

Are there excercises women can do? Is it inevitable in all cases?

What is the determinant?

For example, one lady told me that if a girl doesn't wear a bra when she is younger her breasts will always start sagging, but if she wears a bra properly they should stay perky.

Is this true?

Enquring minds want to know.