Thematically, magic is loosely based on D&D style Vancian magic. Spells often require a predetermined set of actions and or materials to cast, with the general rule being more complicated the action and more expensive the material the more powerful the spell. Of course, for the sake of the RP this material limitation purely thematic... Unless You're constantly casting a spell that requires ludicrously rare materials, then I might say something. As for power, well, continuing on the D&D comparison I'd say an old wizard would be the equivalent to a 9th-12th level wizard. You can cast simple spells like fireball pretty willy-nilly and you can cast 'battlefield' changing spells with decent effort. Unlike D&D how many spells your character can cast is only limited by 'exhaustion' and that really only comes in effect if you cast spells at the limit of your power.
With all that said, the magic system is a work in progress and I'll work with you to create a balanced character should you go the wizard route.