On the flip side, girls it have really really easy on their early 20s. That might create an "suply is infinite" kind of thinking in girls, and maybe perhaps even a degree of narcisism sets in (I am demanded, I deserver x, and y, and of course z qualities on a bf/ideal partner). Some girls just fail to realise that past 26 (maybe 28 for asian girls), looks tend to fade. (fertility peak is 22).
So, absent a family presure, it is easy to get comfortable thinking this attention they get is normal, and will last for a long time.
Hence, they hit their late 20s/early 30s with extremely high expectations, yet their perceived value has diminished with time (at least looks wise).
Many girls realize this, and end up being in "settling mode", which honestly, if you are a guy sucks. She will not love you for what you really are.
To be honest if I had a daughter, my advice would be find a good one between 25-28. That's where your should be wise enough to know what you want, but still have time to change your mind if you feel it is not the right thing.