I've studied Alchemy myself to some extent. Al thought my experiences were mainly on spiritual alchemy. It is true that a person can expand his lifetime to some extent but immortality is a strange phenomenon.
It is a sword with two edges, you can be bound to this earthly existence but it limits you only to it. Of course, if you believe that there is nothing after death, then my comment would be void in this case. Although if you have any experience in astral projection, you can kinda find an understanding as to what I try to say.