What lv do you have to be to come across a Legend dragon to get the achievement after killing it?

i believe 50 not sure thou

My ch. is a lv 67...still haven't seen one and I have finished the main story and dlc story.

70+ if I remember right. I don't have any characters that high, so I haven't seen them yet. Other beta testers were saying they only found them after 70. Above 60, you get Revered Dragons, above 70, you finally see Legendary Dragons.

My main character was lvl 71 when i started the DLC and i have seen revered dragon (they look and act blind lol) but I still haven't encountered a Legendary dragon through out the 20 hours i have been playing, still got more to do though so I will keep a look out.

When I fast traveled to Morthal a Legendary Dragon attacked and the appellation was Jarl Idgrod Ravencrone. 0_0

Level 71 in 20 hours?
Someone has been power-levelling and probably abusing some glitch or another~

Also, if you clear the main quest doesn't that...you know...stop dragons from appearing?

Use the http://www.gamesas.com/forum/196-dawnguard-cheats-hints-and-spoilers/ for this kind of topic.