In the middle east, about of the people are under the age of 30.
half
two-thirds
one-fifth
90 percent

The information I found, from various sources is that around 20, 25 or 30 % of people are aged 15-30, and also that 60% of the population is under the age of 25.

Taken together, this excludes all options lower than 60% (half, one-fith), but I don't think it's as much as 90%.

So I would go with the answer "two-thirds".