I'm 12 years old. And I weigh only 85 pounds. Sure, I've always been skinny. But I'm slightly worried. My dad is skinny, but my grandmother is worryingly skinny. Is it all in my genetics or do I need to put on weight? I'm 5 feet tall by the way, and turning 13 in August.

If you realize that your dad is skinny, and your grandma too, then yes, probably is genetics. You can bulk up when you are older, but 12 is not the time to be worrying about your weight. You have a lot of growing to do !