I don't think that vein people could go on forever, quite on the contrary. I think those that keep a young spirit i.e. keep curious and engaged could endure longest.

but I think we as a species are not designed to go on forever and I doubt any sentient being would be or rather the perspective would be so different it would be difficult for us to grasp.

In fiction this is a recurring topic- just see the Elb or Eldar in "Lord of the Rings"...

the die and fade from the world as they have seen everything and do not continue to have children (how many children can you see dying before going insane?)