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Astronauts on the ISS age slower, a couple of miliseconds per year. They age slower because they are moving faster and they are also aging faster because they are in a shallower gravity well than earthlings. When you add both together the first effect prevails.

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I reread the article with a little more care and as a result of special relativity the satellites "fall behind clocks on the ground by about 7 microseconds per day" and as a result of general relativity "each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day". So that would mean if the ISS was orbiting at the same level as the GPS satellites the astronauts would age faster, but since the ISS is closer, they age slower.

It is not the height but the speed. They would be moving so much slower in a higher orbit.

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