
Yes, the Sailor Guardians start out 14/8th grade (13/7th grade with Minako in Codename Sailor V manga) and the series ends with them at 16/10th grade in high school.
I can't find the old "14 years old = Usagi, 18 years old = Konata" image macro (it's a great example!), but SM's looks is partly because the character designs are shoujo. The "panty shots" are just the bottom half of their leotards, and the body lines (which DIC/Cloverway censored--Usagi never had any to censor) honestly isn't any worse than a Barbie doll.
Keep in mind, back in '92, THIS was the target audience (the manga was pre-teens to teens) for Sailor Moon, although the fanbase gradually became THIS within the year, Christmas '93. Nobody expected it to become a hit with adult male fans (all the doujinshi, garage kits, etc, etc,) since Naoko's idea was a combination of a Sentai team mashed with Mahou Shoujo.
Fun fact: A lot of the Sailor Moon seiyuu starred in this gritty show about a year before SM happened! Surprised the cast info isn't filled out...