So I’m creating a new NPC villain class for an epic campaign I’m designing and decided to give them some potent abilities. Two of which I would like some input on as if its to much or not a bad idea. Let me know what you think.
Thanks.

5th level with a Dragon.

A Paladin only gets a horse.

Will the dragon, due to age category, have the same CR as the Paldin's Mount or a Summoned Monster from Summon Monster III?

I think you should move this up a few levels to 14 or 15 and then get pretty specific about the age category of the Dragon. Don't forget, Dragons age slowly. The age category one has at the beginning of a 20 level campaign is likely gonna be the one at the end of a 20 level campaign. Maybe consider allowing class levels. But then, OMG, how will you keep it balanced?

my idea is the CR of the dragon should be the same as the riders CR.
as for the aging issue I added

also, these perticular knights are only found on the plane setting i have created for the campain.

and i agree that 5th level is a bit soon, i changed the dragon mount to 17th and the binding to 19th so only the highest level knights gain the new special mount.

I also changed the dragon mount some what

not bad but what would you do if I as a player wanted to bond with a draco-lich. Assuming I am something like a death knight or half-vamp or really evil cleric and wanted to enter into this class would you allow it or is it for fighter types only.

the class is open to only paladins or blackguards. To become a Chaos Knight the initiate must undergo a rather grotesque ritual, which involves days of preparation.

the dragon ridding chaos order of the blood flame are meant to be NPC's

as for chaos knights else where in the planes, the mount type should be left up th the GM. the binding ceramony is a special feature of the chaos order of the blood flame which is found in an epic level campaign series im writing and will be game testing in the not to distant future and hopes of possible publication.