Quartz said:
Just a thought, but instead of delaying spellcasting so much, how about delaying the advancement instead? You could do this by mandating multi-classing for the first N levels such that no more than half the levels can be in a spellcasting class and that you cannot take the same class two levels running.
I'd really, REALLY recommend against this. Restricting what the player will do down the road (i.e., railroading) tends to be EXTREMELY unpopular with most players. Even if it's effectively the same as saying "Caster classes don't count with respect to Favored Class", and even if in the long run it's the same as requiring a couple non-caster class levels first, it FEELS different to the players. A player should have more options as they level up, not fewer.
That being said, it's not an unworkable concept. How about this:
Each magic prestige class requires THREE Feats, which the player takes as he gets closer to the casting level. Each feat unlocks a bit of low-level casting.
Talent I is a Feat has no requirements and gives a little cantrip-level ability. Pick three cantrips/orisons for one spellcasting class, and you can cast them 2/day. (Since Psionics no longer has cantrip-level abilities, use the existing feat Wild Talent instead)
(This is the one I use already to unlock my PrCs.)
Talent II is a Feat that requires Talent I and 4 ranks of a related Knowledge skill, depending on which caster class you picked for Talent I (religion, nature, arcana, or psionics). It gives the remainder of the 1st-level cantrip ability; Wizards/Druids/Clerics know all cantrips/orisons and can cast 3/day, Sorcerers know 4 cantrips and cast 5/day, Psions get 2 PP (but no bonus for INT) and knows two 1st-level powers.
Talent III is a Feat that requires Talent II and 8 ranks of the Knowledge skill. It gives the remainder of 1st-level spellcasting (the 1st-level spell slots, the remaining known spells, and bonuses for prime stat).
After taking three Feats, the character casts spells exactly as if he were a 1st-level caster, even though he hasn't taken levels in any "caster" classes. Humans could enter a PrC at level 6 (8 skill ranks requires 5 non-caster levels), other races would have to wait until level 7 (three Feats requires 6 non-caster levels). All you have to do then is shift the casting ability up one level; that is, the first level of the Wizard PrC combines the spellcasting of a level 2 Wizard (2 first-level spells, 4 cantrips) with the other 1st-level benefits of the Wizard class (Familiar, Scribe Scroll).
The idea is, this avoids the "Magic Missile" issue by letting the player have that ability relatively early (level 3), at a time when it'd still be useful. And, it lets them ease into the class a bit more. I'm sure it needs a bit more balance, of course, but if you combine it with the Focus/Manifestation skill concept I mentioned before, you'd probably end up with something balanced.