Okay so before I told fellowa that obviously he must be wrong, I first decided to test it.
I made a Death Knight Lizard with Rage and fought the Voidwoken Voidlings on the beach. I used Rage on my first turn, leaving me with 2 AP which was not enough to actually reach the enemy, so I ended my turn and let the enemies come up.
The OP is wrong and it does not end on the same turn you use it. Rage does persist for the following turn, with a 0 turn duration, so you can have a full 6 AP to use attacking.
