The desire for immortality is a common one, given our innate fear of death. We share the same desire for immortality of our characters. Potions of immortality are often fakes, while spells of unending life invariably turn the caster into a vampire, or a liche or some other evil creature.
What if there was a genuine 'potion' that granted the consumer longer life? This could be as mundane as simply drinking elven wine to something as exotic as spice harvested from the lairs of dragons. Each dose added some years to the consumers life, but only to a certain amount. Immortality requires regular doses of the 'potion' with a frequency dependant on the strength of the potion. Dragonspice might only be needed once in a decade, adding another 10 years of youth and vitality to the consumer, while the elven wine would need to be comsumed daily.
How would this change your world?