A professor I met with at the Weizmann Institute had a thoughtful explanation for why Israel is the ONLY developed country in which FEWER 25- to 34-year-olds than 55- to 64-year-olds have a college degree:
I thought about the statistics you showed me and can suggest a possible explanation:
During the 80-90's there was a massive immigration of Jews from Russia to Israel, a high percentage of them with high education. The number of adults with high education was therefore strongly influenced by this influx of educated people. The fact that your curve shows only a minor decline implies that actually the percentage among Israeli born actually increased.
Indeed, there was a major increase in the past decade with the "college revolution": tens of new colleges were opened, effectively DOUBLING the number of students in the institutes of high learning
I wonder what the numbers would look like if one only looked at people who were born in Israel?