If you're looking for a way to be free of the effects of aging (undying) then you can create an Oath of the Ancients paladin (PHB 86). Paladins get the Divine Health feature (making them immune to disease) at 3rd level, and Oath of the Ancients paladins get the Undying Sentinel feature at 15th level:
Starting at 15th level, when you are reduced to 0 hit points and are not killed outright, you can choose to drop to 1 hit point instead. Once you use this ability, you can’t use it again until you finish a long rest.
Additionally, you suffer none of the drawbacks of old age, and you can’t be aged magically.
Basically, you'll need to be killed in some way in order to die. It fits well with the idea of the archetype, too.