I'm concerned no-one has suggested a Dragonwrought Kobold yet. It ticks all of these boxes:
* Must be a true dragon
* The dragon will start at max age category. (I debate using the epic rules on dragon progression or not.)
* The dragon must be a master of all arcane.
* In addition to his draconic HD the dragon has 21 character levels to play with.
* Wealth, Time, and Resources are effectively limitless barring bending space time.
* The dragon must be immortal and immune to the effects of time. (DM's words, not mine.)
* Sources are pretty much anything within reason.
It would probably not be as powerful as a Great Wyrm thingamagincka dragon (Isn't Force dragon the most powerful?) but it would be fun having the PCs fear the "dragon" all the time, and when they finally meet it, they face something little bigger than a house-cat, who then proceeds to beat their asses.
What about making the dragon a master spellthief or a rainbow servant (this does need a refluff as an evil rainbow servant)? So not only does it fight like a dragon with loads of sneak attack dice, it also has a caster level of around 500.
It'd be something like this:
Great Wyrm Red Dragon/ Master Spellthief 1/Wizard 1/Bard 1/Sublime Chord 2/Rainbow Servant 10/Assassin 1/Knight of the Weave 1/Beguiler 1/Warmage 1/Dread Necromancer 1/Some Arcane Casting Class 1
Sure it wouldn't have a lot of spells, but the ones it had it would cast at something like caster level 400, and it could get wings of flurry and Consumptive Field perfectly well.