You do need high inteligence to learn higher level spells.
Meteorstrike, a level 19 spell, requires you to have 12 Int to learn. At level 9, I have 15 Int (12 base, 1 Know it All, 2 gear).
Honestly, the level requirements are unneeded; all you need are the skill and ability requirements. Skill gating works better than level gating, two people with equal Intelligence should not have the access to the same level of spells if one has 5 Fire and the other no points in the skill.
