I don't think there is a single moment where a woman wakes up one morning and they have magically "hit the wall", it's more of a process and there are various different stages of this happening. Belle is certainly past her peak or prime but she is ways away from being a used up wrinkly roastie, to say that she has fully hit the wall is delusional but also to say that she still looks as good as ever is delusional.
Some people lack critical thinking skills and when they hear someone say they are past their prime it means they are not attractive anymore, but that's not what's being said, it's just that as a comparison between Belle from 6 or so years ago to the Belle of today old Belle was hotter/more beautiful than Belle of today, that doesn't mean Belle of today is unattractive, she's still pretty hot, just not quite as hot as she once was.