Probably fairly common story.
Women have always be more body conscious ... more than guys anyway.
And al the pictures of beautiful perky tight, but photoshopped, women in the internet won't help.
That said, I have seen young women with large and not so large cup sizes that are sagging (a lot). Though with larger cup sizes it will be more obvious.
When looking at my SIL's breasts (E or F cup) and comparing them with pics I've seen of her in her late teens, early 20'ties, I can state they do hang a few inches lower ... which absolutely does NOT mean they are not gorgeous (but off limits 😉
When my wife is topless or naked in public, she is aware that her C-cup is not as pert as it used to be, but she's still proud that they do not dag too much AND they've nursed 2 kids. And she enjoys the attention her breasts still draw.