You'd think they'd be better wizards, having studied magic for longer, rather than being desperate to sign on for a pension
I'm not so sure the cost decrease goes far enough to be honest. The afflictions are a little too random - a mage can last for several years with nothing but a limp and a chest injury, or he can die a couple of turns after you recruit him. If he gets disease, he's doomed. If he gets feebleminded, he's useless.
A little more predictability would go a long way to rebalance the situation, even if it upped the price slightly. Perhaps restricting or reducing the chances of the more serious afflictions (disease, feeblemind) until severe old age would work, though preventing them from occuring within the first few turns the mage is around would help.
I also think it's a bad idea to have age on a pretender. I mean, they're not going to be much of a God if they're half senile before they start. Then again...