How big is a dragon?

I know from the Monster Manual “Dragon Age Categories” table on page 86 that a young dragon is “large”. Which means that if you play on a battle map, he takes up 2×2 squares, which 10 x 10 feet.

What I don’t know is how “large” is measured. Is the dragon just 10 feet wingspan, or 10 feet from head to tail? Or is 10 feet about the length from shoulders to rump, with wings, head, and tail not being counted? I am trying to 3D print a dragon miniature, and for that and a better description I really would like more about how big a “large” young dragon actually is. Anyone got a source for that?