The second picture is toward the extreme end of the long and large body. Some artists get their proportions completely off and make the hips and legs inordinantly sized, or inavertantly shrink the head. I'd bet the second artist worked his/her way from that sort of proportioning. I think there's more contributing to the first's youthful appearance, such as the shine and roundness added by the color, and her hips being somewhat masked by loose clothing. I agree that her head is slightly large, but not alarmingly so, and I simply don't buy her as a **22** at all. She's too developed in the hips legs and breasts. If you made her legs slender Sailor Moon sticks, took away her breasts and narrowed her hips, then I'd agree, but it's too much of a combination. Another mark of age is flaw. Scars, pours and basic texture granulation. Now lots of anime is colored in a fashion that excludes this, and true, it doesn't make, say, Nurse Nanako look like a **22**, but it certainly doesn't hurt her look under twenty. I just think this idea is sharpened in this particular picture and if we could find her inked only she'd look a tad older for you. Just my opinion.
I certainly respect yours, Herald. You taught me a thing or three about anatomy!