>>89886040I guess I don't consider 14 a "child," at least when it comes to voice acting. A minor, yeah, but by the time girls hit high school they pretty much already sound like they will as adults when it comes to pitch etc.; voices don't change as much for girls.
The contrast between her design and her voice is what works for me. She looks younger than what her age actually is (most of the characters in this show do), but the voice gives you the idea she's not supposed to be a little kid and so you can adjust. Also the outfit in contrast to her age works well for indicating maturity/oddness-- you wouldn't expect someone of her age to dress that way, and yet she does 'cause she ain't from 'round here, etc.
Also on a more bullshit symbolism level you can argue that Stat not having a sugary sweet little-girl voice works on the level of "what you see isn't always what you get."
I don't know if Star's voice is deeper than Marco's, but being a teenage guy his voice can and will change in the future while Star's won't.