Whoops, good call. Point of safety for an Ancient Black Dragon then would be 880/6=146, which is a bit harder for a young mage to achieve.
It takes like 15 minutes to get to CL 15. If I had a high damage wand with sufficient charges and 20 squares between us with nothing else to worry about, I'd absolutely attack that dragon. They breath rarely, and with attenuated breath, even if they double breath right at the beginning, you're in no danger. I'd be worried about it making it to melee range--it has to die before that happens--I wouldn't worry about the breath attack at all.
Breath attenuation is nerfed in 4.1. It no longer does essentially zero damage at max range, so it's probably better to let it be. It's just one DL 40 monster. It's not likely to have a game changer artifact or anything.
Ancient Ds cast spells 1/6, and the breath attack is one of 3 (or 4) spells? As long as I can survive 1 breath and can kill it before it gets to melee range, I'll attack. This was true even pre-attenuation.
Breath attenuation is nerfed in 4.1. It no longer does essentially zero damage at max range, so it's probably better to let it be.
No idea when this changed, but yes I learned that recently. Thinking dracoliches were now xp pinatas, I engaged one in ranged combat from a big distance without nether resistance, and was surprised when my hps went down from 545 to 109 in a single nether breath. And that was with a dracolich at 70% health.
i'm getting contrasting opinions here. Some say sure, it's easy, go for it, some agree that it would likely have killed me. (rAcid, no temp resist)
It depends on how many HP you had and what the local terrain was like. If you had enough to survive one breath, and the ability to escape if that one breath did come out, and enough room to be able to engage in a ranged fight, and a source of temporary haste, then fighting the dragon would have been a good idea. That's a lot of ifs, but they're all things that you should be keeping in mind all the time anyway.