It's worth noting, though, that people think of it this way because that's historically what life extension has looked like. I'm still ultimately in favor, but I see a nontrivial chance of a disaster scenario where "keep people barely alive till they're 150" is the low hanging fruit.
Often you can't opt out. My great-grandma was basically non-functional for her last decade: she couldn't move without assistance, couldn't taste anything, and seemed to be in constant pain. But her dementia came first, so by the time we started worrying about it, she couldn't think clearly enough to make any decisions about anything. We never put her on life support as such because we were pretty sure she wouldn't have wanted it, but there was no specific life-sustaining intervention to consider withdrawing, just a bundle of meds which each meaningfully improved her quality of life. So she kinda bumbled along in a cloud of permanent confusion and misery until the end.
