After completing all broken valley and sentinel island quest, you should able to reach lvl20, that the level when I face Laiken. But I did try to fight him before at lvl17 or 18, and its not actually hard at all, with Sassan focus healing me. So I guess you need to work out on your equipments and skills. And beside that I found that killing Laiken only will give you exp of 1 kill, where as killing the demon, Razakel, you get the exp of 2 kills, at lvl20, I get 1286exp times 2.
