age isn’t a disease. it can’t be cured.

True, but every old-age thing that kills you is a disease.

Also, in theory, every part of the body can be replaced with a freshly-grown one as needed, although transferring one’s mind into a new brain may be difficult.

personally, i think it’s cruel to do it by harming other beings, which includes most animal trials.

No doubt, but there really isn’t any way to make progress in medical science without testing things on an animal of some kind, and using unwilling human guinea pigs is probably even worse.