Arcane Lore and Arcane Discipline
In the Arcane Organization file you posted, it mentioned that aspiring spell casters had to learn Arcane Lore and Arcane Discipline before they could learn spells. I think that's a good system that we should use. I also think that our casters could be assumed to have those lores, perhaps at +5 or +6. If we have young someones whom we want to train to be casters, they'd need to learn these two lores first. If they can't get to +5 in both in the first year, then maybe they aren't cut out to be casters.
I like the idea is there anything else that needs to be a prerequisite?
Not really. Here's a link to the pdf on ProBoards. Harn says Family, Aura, and Sunsigns affect whether you get accepted by a Master. I don't think that necessarily applies to us. There are some rolls to determine whether your talent is in the same convocation as your Master. If not, you can study on your own or look for another Master. We can choose to use whatever rules we want.
https://newarakus.proboards.com/thread/2485/guild-arcane-lore-organization
I think there should be some minimum expectation for Intelligence, Wisdom, or Will (or all 3)
I agree for adults there should be a minimum, maybe an average of 7? What if you start training as a child? Would there be a minimum?
I like the idea of having 20 points in all the of those stats to learn. That way your better then average in two of those stats or if your really high in one stat. You can learn it. But it allows for there to be differences in caster and their stat make up
Ok, so 20 points, 21 points. Not much difference.
"What if you start training as a child? Would there be a minimum?"
I think children shouldn't be able to learn Arcane Lore (except in some very exceptional circumstances, maybe) and a child who eventually wants to become an Arcanist should be spending time improving their Intelligence, Wisdom, and/or Will so that they can start to train as an Arcanist once they come of age.
I think the apprentice/squire track usually starts at 13. I could see the same for casters. They’d spend their early years getting their stats to the right level and learning A Lore and A Discipline.