Eh...In the end it's your story and you should tell it the way you want to tell it, but I'm still shaking my head at the Fountain of Youth. I just feel it would be a lot more interesting if each time they used magic they knew they were a step closer to death. It doesn't have to be a fast paced type of thing either, think the WoT with the magic slowly turning them insane. The guy could easily still be alive to train a younger magic user if he wasn't going all Dirty Harry on everyone with his magic mojo.