Question: How old is Edward?
Answer: As the other response says, the number of years is never stated. Physically, I think he is supposed to look about twenty years old. Bill wants him to start a proper business. None of the adults seem to think that he should be in school.
Question: If Old Man Marley is actually a nice man (and not a "shovel slayer" as Buzz claims) then why does he always give Kevin that cold, creepy stare? After Kevin ran away the first time wouldn't he want to talk to Kevin the next time, to assure him that everything is okay?
Answer: Because he's understandably angry that Kevin's so unreasonably scared of him and assumes the worst in him without even getting a chance to know him. He never gets a chance to talk to him, because he always runs away too quickly. The first time he gives him that stare was when Kevin was watching him shovel from the window. Nobody would like to be stared at like that while doing a simple task.
Answer: Marley appears that way mostly because the audience sees him from Kevin's point of view. Marley is miserable and sad because he is estranged from his family, but we see him as a crotchety, unpleasant person because that is what Kevin believes. Buzz had tainted Kevin's opinion of him by spreading the false stories that a gullible Kevin believed were true.
Question: Why was McClane introduced in the first Die Hard movie as a New York badge, and in the second Die Hard movie as a L.A. badge? Then in the third Die Hard movie, he's again a New York cop.
Answer: In the first movie he's a New York cop visiting his wife. In the second Die Hard, he tells the airport officer that he's LAPD and moved there because of his wife's job. In the third Die Hard film, he most likely went back to New York because of marital problems and became a New York cop again.
Answer: It is never stated.