When you learn that the Peace of Westphalia ended both the Thirty Years' War and the Eighty Years' War, you start to think, what other wars are only named after their length? You might also wonder why historians couldn't get a little more creative, but I'm only here to help you answer the first one.
The single digits years have three sets of twins! There's a Dutch/German Three Years' War as well as a North American one. The Seven Years' War comes in both a worldwide version and one just for Scandanavia (and maybe even more), while for the Nine Years' War you can choose between continental Europe and Ireland
Sometimes you can't get it all done in under a decade, though.
Cuba had a Ten Years' War caused by a sugar mill owner, Poland and Prussia went with thirteen, and since that wasn't quite enough the Holy Roman Empire drew all of Europe into the Thirty Years' War. Burma brings us the Forty Years' War, Spain lost the Netherlands in the Eighty Years' War, and England and France inch up to a century with the Hundred Years' War.
The kingpin of all temporally-named wars is the Three Hundred and Thirty Five Years' War, fought between the Netherlands and the Isles of Scilly. Despite spanning centuries, not a single person died and not a single shot was fired. The conflict began when a grumpy Dutch Admiral declared war out of frustration, and was unimportant enough that no one cared enough to put together a treaty until a local historian contacted the Dutch Embassy in 1986.