Just finished the Final Empire, have some questions.

Recently finished the Final Empire, where it was revealed that the way the Lord Ruler was immortal was by combining Feruchemistry and Allomancy.

Now here's what I don't understand, by storing his Age, and burning it with Allomancy, he makes the effect stronger, so usually where it would only make him younger for a year, it would make him younger for 10, but If that's so, where does his supernatural healing come from?

And it was mentioned that he was flayed, crushed, and even burned until nothing remained but bones, and in all of these scenarios, shouldn't he have lost access to the metals that kept him immortal, since they weren't in his possession?