Board Thread:Skyrim/@comment-13670863-20130728082525/@comment-6881629-20130728121848

The Elder Dragon should start to appear at about level 36 (on the standard difficulty) you can spot its Elder by the copper colour scales and their head looks a bit like the Dragonplate Helmet, their not really rare though before the DLC they were the hardest type of Dragon once you got to a high level at they were all over Skyrim.

If you have Dawnguard and want a real challange against a rare dragon you want a Legendary Dragon they only start appear after level 78 and even at 81 i had to turn the difficulty up to max before one finally appeared (theres even a Trophie for taking one down).