This is an older person's way of telling you to "get lost". I hear people say this all the time, but I have no idea where it comes from. Some people falsely believe it's true, while others say it just to make you go away.
While the first part may be partly true, I have on my auto policy to specifically exclude drivers under 25 (in order to reduce my rate). I can probably share the certificate of insurance with you if you're really interested.