“He's this old man, on his «last life» and he had no clue what he was going to get. He regenerates into a youthful and energetic young man.
Its easy for him to get excited and forget sometimes that he's really old. He feels young and he's got the body to match his enthousiasm.
But there are times when the old man comes out, in between the youthful vigor. And when it does, it's sometimes terrifying. Because you realize that this old man would stop at nearly nothing (including mocking around with his best friends timelines) if it means his preservation.”