[quote=Altered Tundra]
Who says they don't? I didn't see no rule about how dragons couldn't exist. If talking frogs and talking dogs can exist as summons, surely talking dragons could. Plus, there's a fucking jellyfish sage. If there could be one of that, surely a Dragon sage wouldn't be out of the question. xD
[/quote]
*would like to point out that frogs, jellyfish, and dogs are living creatures. Dragons are myths.*

But for the sage thing, I thought you had to have a really close relationship with your summons to become a sage. Then train at their home, then of course you have to take in chakra, and take on some characteristics of your summon? Isn't becoming a sage much harder than just...being friends with a summon?