WotLK I can't use my fly mount (frostmourne)

[IcyGerberBait]

So even after getting my expert riding and getting a gryphon I can't seem to ride it, it doesn't let me mount it doesn't matter where I am just says "can't mount it here"
Is that a bug? am I missing something or what?

[skullatbash]

you need this: http://wotlk.cavernoftime.com/spell=54197
"Allows the player to ride flying mounts in Northrend."

[Thorbjorn]

You need a lvl 77 to train it on your first character. On your second you can buy a heirloom book that he can use when he hits lvl 68 to fly in Northrend.