What is the average IQ of a 16-year-old girl?

By definition, the average IQ is always 100. IQ scores are always adjusted for age to keep the average at 100, but above age 15(?) intelligence remains static till age 55+. The scores are usually arranged in such a way that half the population has scores in the range 90-110, and 75% in the range 85-115. Obviously, it is possible to devise scoring systems that minimize or maximize differences. This is particularly obvious at the extremes: one can arrange the scores so that 96% of the population is in the range 60-140 or one can spread the same people over the range 50-150, for example.