Currently the only method of knowing is "#o what are your ESS WIL INTEL attributes?", and then comparing them with some kind of magic number (which I don't know
Instead I suggest, a new object, lets call it "Orb of Mages" or something like that. You give this object to a person, and he uses it. The object then calculates whether the person can learn or not, and gives a message like "You don't seem able to control the magic inside the orb"
or
"You seem to have some control over the magic inside the orb"
That way we'll have a good Rp reason to say no.