Lilmod, I really can’t dispute your points, since both of us are talking based on our own experiences, which obviously represent a small sample size and may not reflect what goes on in general.
I still don’t think that Israelis start dating later is an issue- just like some wait until 2nd year Pesach, there are also some US girls who wait until they calm down from the seminary high, until Chanuka or Pesach of the year they come back. And although there are girls who stay in the US for seminary and may start dating, there are also girls who stay 2nd year in Israel and start even later. Just like in Israel, there are those who start right away and those who wait. And if there is a tendency to hold back girls, it will shift the age only a few months- parents may hold back a girl born in Oct/Nov/Dec – so instead of being the youngest in the class, she will be a few months older. In any case I know there is this trend now, I don’t know if parents did this 20 years ago.