Question: Why do you think the girls are still drawn at girl height, and not women even in Stars? They are usually much shorter than the adult characters, even though they're 16.
I doubt very much that it was ever a consideration. I’d be surprised if anyone ever thought about it. The anime has a lot of strengths, but being consistent with height, even internally, is not one of them. The character heights are all over the place all the time. Pretty much the only thing you can reasonably rely on is that Mako will be taller than the other Inners, and even that’s not always a guarantee.
I wouldn’t recommend using the anime’s appearance to determine much of anything beyond – maybe – general guidelines. Envision what you like and just roll with the rest.