I assume from the OP that your meaning was that of a person who feels they have lived long enough, and are just bored with life, or just plain tired of living. I have often pondered that situation. If science could discover a way to allow a person to live forever. Would there come a time when you just longed to escape all the drama of life and make your exit.
It seems like eventually you would become weary of the day to day doing household chores, running errands, maintenance, trying to find a movie you haven't seen a hundred times, etc..., and your "been there, done that" list would make your eyes water just reading it.
I think I would end up like Noah. After 600 years I would build an ark just for something to do, flood or no flood. After checking that off my bucket list, I'd probably just go join the dinosaurs.