A phrase tapped onto a noun giving the object in question more significance, or importance. The object in question does not need to be relatively big or old.
It originated in the south and has spread throughout the US.

when you're hungover as shit after a spending a night drunk as a skunk

In the south used, by rednecks, as a tool to emphasize nouns. This term of slang is working its way up the west and east coasts to be used in the Yankee states as a tool to emphasize more intelligent nouns

A man that has a 6" or larger penis.

Another word for large/it's not big nor is it large