The law stating that all first-born children have to be legally named Gregory and are not allowed to change their name until their 42nd and a half birthday.
Gregory: Hey Gregory, are you 42 and a half yet?
Gregory: Not until next April.
Gregory: Well then according to The Gregory Act of 2019 you have to wait til then to change your name.
Gregory: Darn!
Down the old Gregory comes from the cockney rhyming slang, 'Gregory Peck', meaning neck. So down the 'old Gregory' simply means down your neck. It's most commonly used when referring to drinks.