As you note, narrow hips for a female would be pre "sexual-maturity" so that is why your predicted age range "16 and 26" seemed so odd. You didn't want to talk about outliers, but a narrow-hipped female pre "sexual maturity" between 16 and 26 would be fairly rare, even for Asians.
Competitive runners come in two general types, sprinters and distance, that's because running comes in two types anaerobic and aerobic. Sprinters are actually quite short. Usain Bolt was a freak of nature. Tall sprinters usually don't have the high leg turnover that shorter sprinters do. Usain was the exception. Long distance runners also tend to be shorter than the average human, for efficiency. You want to carry less weight, so thin and short weighs less. Just look up the heights of all those African world record holders in the marathon, 10k etc.
Swimmers do tend to be taller, because length in the water is faster. Longer means less drag. It's the same with boats. Longer boats have higher speed potential. Also, taller swimmers have bigger paddles, hand and feet size. Ultimately, for swimming, height has little correlation with efficiency, but the physics of it. A longer body has less inherent drag. Efficiency in swimming usually refers to the mechanics of one's stroke. The ideal swimmer would be tall, and have big hands and feet, and actually a little chubby wouldn't hurt. More shaped like a penguin. That's because fat floats. Swimmers use some of their energy for buoyancy. The more fat, the less energy you need to waste on buoyancy. Also, fat can give you a more streamlined shape. Remember when swimmers, both male and female wore wetsuits to swim? The wetsuits not only streamlined a person's shape, but also added buoyancy. Women long distance swimmers have less of a gap to their male counterparts because of their inherent higher buoyancy. About 5% to their male counterparts. In running, the gender gap is about 10+%. Different sports, with different requirements.