@littlek,
Although I'm not sure your photo is current, littlek, and although Johnson is at an age where a year makes a big difference to a teenage girl's body, I'd have to agree with you. If Johnson looks reasonably grown up, it's mainly not because of her curves, but the shape of her face.
Granted, her makeup and her hairdo help in this picture, but it wouldn't help most of the Chinese gymnasts enough to look like women, not girls.