I was at the same level when I beat him. He is a bitch.
If it gets really hard I suggest going back to Rabanastre and buying that accessory from the clan vendor that reverses item effects. (Nipo-something) A remedy should give you an advantage over him for awhile. Make sure to buff yourself too. The end of the battle can get rough, so if you must use a quickening wait til his health bar is really low (he'll start using Master Eye).