I've always been thin. Two kids later it took some effort to regain the shape and muscle tone that came effortlessly when I was younger.
I'm 27, 5'7.5", 34A, 26, 35. While the ratio may be off, exercise and a sensible diet (gluten free because of celiac disease) I smile whenever I look in the mirror and whenever I chase my wonderful kids around the playground. A little effort and some determination make such a difference.