Before mid-HS, my girlfriends were always size 2-4 maybe 6.
Starting mid-HS, I didn't date women less than a size 10 except as an extreme exception.
Curvy hourglasses with full hips and breasts are hard to find, hardbodies with such are rare (but do exist). I don't really have an "ideal" but most women I love fall between size 12-20 -- with some as low as a rare 6 or as high as size 24+ if their body really has curves and the weight distributes well.
When I met my wife, she was 19 and an anorexic/starving-herself size 6 with a 36C bust.
She's been as large as a size 18-20 with a 42044F.
She's currently around a size 14-16 with a 38-40DD.
I don't think she'd be healthy below a size 10-12 and 38D.
Many full figured women can't maintain sub-size 10 once they exit their teenage years. Supermodel
Kate Dillon, hearlded as the "Next Cindy Crawford" kept starving herself to maintain a size 6 as a teenager, but she couldn't do it as an adult. She could probably still be healthy at a size 10 if she wanted, but she's fine being an active size 12-14.
Dress sizes, in general, are a poor form of figure. "Petite" addresses the 50% that are "straight'n narrow" and the "full figured" addresses the 40% that are "pear/bell" -- a lot of women with curves in all sizes are "left hanging to dry."
If you are an apple**, you're going to have to wear a larger size for your bust/shoulders, and then that makes you look bigger -- especially if they were designed for a pear/bell, that's the
exact opposite direction your figure goes!
If you are a hourglass**, you have to wear a larger size that totally hides your inward curvature around your stomach. And if you're a full-figured hourglass, well, you're really screwed over!
Kinda sad if you ask me -- all those curves wasted. That's why I tailor many of my wife's dresses after she buys them. Yes, I'm a little "home-ec husband" for my wife in many regards when I'm not traveling. I love it because I get to feel up her curves and really entice myself -- especially in public!
**For more generalizations on the female figure and all its forms, see my post/poll:
Female body shapes, width and sizes ...
http://board.freeones.com/showthread.php?t=69141