I've had at least 4 corrective plastic surgeries, 5 if you count the skin graft, as a child, plus 2 minor corrective surgeries since I've become an adult. That would total up to a whopping 7 operations that 'technically' count as plastic surgeries. All were technically elective. But I tend to not class them in with the nose job/boob job/liposuction. All were issues that I'd happily have repaired if they occurred in my kids, and issues that wouldn't have required a book to explain to my kids. "Mommy's going to have a tumor removed today". End of story.
I think the same goes for a lot of physical wear and tear. It's easy to explain that to kids. Heck, their dad may be going in for a nose job soon, that'll be a snap to explain, since it has nothing to do with daddy wanting to be more 'beautiful', simply wanting to have his crooked nose fixed so he can breathe through it.
Repairing the ravages of time and gravity, well, I think that tends to fall somewhere in between. But, having gone through so many surgeries, i have a hard time imagining how bad it would have to be before I'd be willing to do anaesthetic again.