Hrm. Since it's D&D, there's a set of 4 choices that are the standard 'go to's' of beating old age as an Arcane magician.
Lich - downside is you're undead, the ritual is evil in aspect, and you forever cease in character level advancement.
Shade - you become a plane of shadow aspect Outsider, cheat aging but have new minor abilities & weaknesses and also cannot advance in character level
Clones / Simulacrum / Possess target body (replacement) - a great way of cheating death and old age through body swapping, but each swap typically reduces your character level by one. which can be regained through normal experience gain methods.
Construct - through magical means or prestige classing, you become a construct which is immune to age effects (natural or otherwise) but has the downsides of unique benefits and weaknesses, depending on route chosen.
The big thing is Arcane casters have access to polymorph and shapechange magic so they could ultimately care less about what their new 'natural' form might be, related to the path they pick.