My destruction skill is at 31, and to cast apprentice spells at half magika it needs to be 25. I just leveled up, and I already spent a perk on the first portion of the destruction tree. Why wont it let me spend a perk on apprentice destruction spells when I have a skill of 31 and the prerequisite for the next portion of the tree? I am playing on the PC btw and have not used any console cheats.

I figured it out. Even though i spent a point in the novice spell casting, it didn't quite go through for some reason. Fixed.