This is a question about the same magic explained in this one. I also explain the magic below.
In my fantasy novel, magic is a natural part of the world. It is not some mystical force shrouded in mystery, but rather backed by science (though only I, the author, know it's true workings).
In my world, magic is a force that by its nature changes living cells. It is similar to radiation, but different in the respect that it changes what the cell does, usually in a beneficial way. For example, if the cells of an eye were exposed to magic, the magic might make the eye also see infrared light.
There are those in my world who can control the change worked by the magic. (They can force the magic to make the eye see infrared light. They can also use magic to make that same eye go blind.)
If this magic were used on humans (or elves, which have basically the same physiology), could it be used to increase their life span? If so, how would that be accomplished merely by altering what the cells do?