My mom says im still too young to be vegetarian?

So 2-3 days ago, I asked for advice on how to tell my mom I wanted to be vegetarian. Well I talked to my granddad to day over the phone, and he agrees that I'm too young to be vegetarian! He also said that I need meat and fat to grow (okay, ew) and that I am still growing. But she won't listen and I have even done my research! That's what I've been doing with all my time. But my grandfather also says that there are vitemins have paracites or are bad. He said something like that and that I had to be careful with vitamins. HOW DO I CONVINCE MY MOM AND GRANDFATHER? This choice is what I want, but they WILL NOT listen. By the way, I'm 13.