Well, either they die or nothing happens since there is no additional category. Though I suppose the GM can just project forward based on the progression of age brackets and their penalties.
I say nothing.
It's too powerful a spell for 3rd-lvl if it can outright kill you with no save.
I was wondering whether multiple uses of the spell can advance the target through multiple age brackets and I'm thinking yes up to venerable.
They'd take another hit to their age category and take all the negatives I'd think. Theres nothing after venerable, but you can just make something up. Make the venerable older and weaker and even more decripit. Its evil, its not going to just ignore you because your old.
Thats my two cents anyway.
OH NO, THE ELDERLY ARE PRONE TO DEATH. I think it would be favoritism if it were ruled that those who were not ageless could waive the dire penalties. Yes, it's not as fair as a fireball but there's a reason the society only counts age as fluff. Yes this is old but I don't want one of my party members citing this if they play a venerable character.
I see that 2 cents, and raise a nickle.