I have entertained the idea (if you believe in the quantum many worlds) that everyone will experience themselves as aging to infinitely old age, because in the parallel worlds, well, you don't exist.
If you want a grim take on this looking into the quantum immortality thought experiment. I can't remember who wrote it, I think maybe Chalmers, but the idea is that while the experiencer is immortal, they will still accumulate injuries, old age, etc. It would not be a very pleasant immortality.
Saying that something will happen across the multiverse is stating a certainty, so long as it's physically and logically possible. Every absurdly unlikely thing will happen in that sense. Everybody will, somewhere (and somewhen) become purple with flashing yellow spots. That's very different from saying "I expect to experience this happening", which is a statement about what's probable.