I'm relatively new to D&D, and after playing a bit with some friends, picked up a few books to learn more. In one book, "A PRACTICAL GUIDE TO DRAGON RIDING", I was introduced to the idea of dragons as mounts. None of the usual dragons seemed to interest me, until I came across the Rust Dragon. I really liked the aesthetics of it, and the fact that it could rust metal.
But, I was wondering, could you have a rust dragon as a mount?
I searched this up, but only found mention of rust creatures, not rust dragons...
In addition, (I started to create a serious character for an upcoming campaign) can a character have a dragon to begin with, if say, they grew up with it or met it before the time the campaign is set? (Backstory, basically.)