Most of those claiming that they'll off themselves are deluded. That's what people in their 80s and 90s now said back when they were younger and healthier. But this instinct to live is stronger than any of us realise.
Most people say that's what they'll want to do, but only a miniscule number of old people do it, even when capable of doing so.
When my mum had her disabling stroke, she said she wished she'd never been found (she was unconscious on a stone floor when her neighbour found her, and half an hour away from death by hypothermia according to the medics).
Two years later, when she was unconscious due to an infection, my brother and I were asked what she'd want should a decision about resuscitation be needed. We both said that she'd not want to be resuscuated. It seemed obvious given what she'd said before.
She recovered, and the nurse at her care home asked her for instructions should such a situation happen again. The nurse (stupidly) told her what my brother had said to her, and my mum was furious. She said that of course she wanted to live. And has been telling people that my brother wants her dead, ever since.
She's been hospitalised twice since then, and on both occasions I've been there when a doctor's asked what she'd want. On both occasions,even though the doc has patiently explained exactly what resuscitation will do to her fragile body, she's insisted she wants everything going.