I do not think it's an entirely fair comparison since these art styles are so different. Another thing is that a lot of anime and manga is drawn in rather simplified art-style, where heads and faces will lack nuance necessary to show the age. That leaves only body shape, hairstyle, and clothing as a means of getting character's age across.
Japanese media's genre conventions are also a thing. First character looks like someone from a slice of life comedy manga or anime set in a workplace. Character designs in these usually lean towards being drawn as cute, grounded, endearing, or funny looking. The second one looks like a character form an edgy show focused on action or fanservice, where most characters are larger than life and made to appeal to teenage boys and young men. School uniform with a loose tie, partially unbuttoned shirt, open blazer, gloves, and blonde extravagant hair implicate that she is most likely supposed to be a teenage deliquescent. These characters tend to present themselves as older than they actually are and play up their looks.
There is a cultural element too, where for some reason most Japanese stories involving action and adventure center around characters in early and mid teens. Some say is to appeal to the audience by making characters in stories similar to readers or viewers. For one reason or another the rest of the world makes plenty stories aimed a kids that star adults, and quite a few that go the other way. Another reasoning I heard for it is that high school is the last time in average Japanese person's life where they have some degree of freedom and spare time, so they associate that age with adventure. Either way, that leads to situations where teenagers have physiques of superheroes and are capable of doing the same things superheroes do in American films and comics.
The design in
From The Uncanny Valley's post is ridiculous for a 17 year old however.
