wow same here...I look at my parents now and theyre both quite fit, but they have put on weight naturally because theyre ageing, and my parents were both super skinny right until their late 30s and im like chubby in my 20s. Tis sad indeed.
I believe genetics is such an excuse. It provides a framework for what your body naturally wants to do (hold on to weight, build muscle, etc.) But it's not right to feel limited by it. As long as you eat right and exercise, you can create your own body, as opposed to feeling like you are cursed to look like your mother.