A couple days ago I was talking to this friend about action in animation and I guess here I can extend my thoughts. The poor representation of her above is obviously a simplification of the real image. To create a similarity between both, I had to emphasize in two details: the hair (although I haven´t seen her in a while) and her tatoo. Apart from these two, no one could differentiate her from any other drawing in this blog.

Age for example. Animations have to work with the least number of lines possible. When characters are created, visual aspects like height, body posture, and facial lines define the age of a character. Notice the faces. In several mangas you´ll see people growing old (unlike many American comic books). From childhood to adolescence height usually plays an important role, but from adolescence to an extended adulthood one simple line below each eye makes a whole lot of difference.

The fewer details give a greater liberty in lots of perspectives. With less things to worry about, the borderline of the implausible is pushed further away.

For a further view of this subject I reccomend the last episode of the Evangelion TV series. Animenation´s John Oppliger once answered a question that also might help.