John states that he left home in 1620 when he was 14. But in the episode "Golden Boy", as he's filling out a form during World War II with his 20th century bio, he says his real name and birthdate, in 1607. This means he was only 12 or 13 when he left home.
When John drunk singing in a pub back in 1964, he's using a Shure SM57 microphone, which is not in production until 1965.