Probably fast Sub, there are 'young' children that have a disease that makes them age at an incredible rate, I don't think they even reach the age of 20, because by that time their body would be like 70 years old.
But Xen, are you sure it wasn't just a Siamese twin? One human with two heads, well I have never heard of that. But I have heard of stories of a Siamese twin who shared the exact same body, but they each had their own head.
And it could also be photo shopped or something.