system
Given the following post, respond as if you're commenting on Reddit:
human
[General Fantasy] Why can't you just cast a spell to make you younger and use it again each time you become too old instead of becoming a lich or something?

Even if you must do it every few years, it's not going to get any harder.
gpt
It depends on the setting.

In Dungeons and Dragons 3.5 there's no spell that can definitely make you younger. In addition, lichdom has more advantages than just fighting old age. You can't be killed without your phylactery being destroyed and you get a huge boost to power.

In Harry Potter, the only way to make you younger without side effects is the elixir of life from the Philosopher's stone. It's possible that there'd be fewer horcrux-users if the recipe for the stone were public knowledge. Sadly, it is not. You could potentially use unicorn blood, but that has some terrible side effect. It's not clear what that is, but it's probably comparable to the damage from making a horcrux, and you have to keep killing unicorns instead of just making one horcrux and being done with it. I've heard it suggested that continued use of the polyjuice potion could work, but that might only make you look young.

I imagine in general either anti-aging spells are extremely difficult to impossible or that people become liches for the other advantages it has.