...means Omar was 21 when he finished high school. And three years older than his classmates, who would have been 18, right?
Class of 1966 means 1966 graduation, four years of high school for Class of 1966 means 1962 commencement. So if he had attended for four years, he would have arrived in the summer of 1962.
One does need to read between the lines, we are being lied to up and down and inside out; telling us he arrived in 1963 eliminates the question, where did he get the money from, or make the contacts, that would provide his brother with airfare, living expenses and tuition at a private school. The lie just might give the kenyan student time to arrive in Cambridge, settle in, make some contacts and find a sponsor for his brother.
Problem with Cora isn't only that she's a communist, she has all the records under her control and if you want to see them it's by appointment.
Try a little imagination; the kenyan student and his brother Omar, photographed together. When might that have been taken? They both look older than they might have been in 1964 when the kenyan student departed from Boston - and Omar also seems more than 19 years old, as he would have been in 1964...so it would seem, as Omar never showed up again in the village in Kenya, and the family described him as 'lost' - The photograph dates from the kenyan's visit to the US in 1970-71 and is of the same period as when you see him with zero at the airport in Hawaii.
The result? Omar wasn't lost. They all knew where he was. And when she was old enough, Zeituni also went to Boston. And that's why, when Zeituni was found, they also found Omar.