I am wondering what level you should be to have the mission to kill Alduin.
Im level 12 and Im already at Alduin. Has anyone got the same or am I so fast in skyrim?

Any level you want. There's no rush to finish the main quest and you don't necessarily need to do all the quests consecutively. Play at your own pace.

Welcome. If you feel confident enough to face him, go for it. Its really up to you.

Doesn't matter. He's been killed at level 8 on master, its never exactly a hard or climactic battle, so much as a speed bump.

A snow bear gave me more problems than the supposed father of Dragons.

Same here.