I've seen both of my grandfathers become shadows of who they were due to alzheimers and I really hope I don't live long enough for that to happen to me. Fate worse than death, I think that's reasonable
Living to 120 would be great if that comes from getting four more decades of what my patents and grandparents were in their 60s and 70s: fine day-to-day, but maybe they needed a scooter to do a full day at Disney closer to the end. Not as young as they used to be, but still basically able to do everything they used to, just maybe a bit slower.
Living to 120 would be terrible if you get an extra 40 years in a memory care unit.