i was level 30ish when i beat flamelurker, but i used entirely offensive magic and i only had 14 vitality (low total hp) so i died my share of times. You may be able to beat him sooner than that.
for any item it says you're below the requirements, go into the second screen in the start menu, click on x your shield for example to open up a menu with all the shields you're carrying, then press square over the shield you want to check out. Left to right it lists str/dex/mag/fth requirements (among other things) for using weapons and armor. if you don't meet a requirement it will be red.
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