Some people are naturally thin and some people are naturally heavier. It doesn't mean that bigger is healthier, or much thinner is healthier, it's on an individual basis. ↗
When I started modeling, I was definitely heavier. I was quite voluptuous in fact. I had a real baby face and baby fat. But I was a baby! I was told I had to get into better shape, but I'm quite stubborn so I didn't. ↗