Old people may have a lot of reason to volunteer to use these.
I think we will discover that our body can reset itself via some trigger mechanism. It built us once, the code isn't gone. It can do it again.
There isn't a single species that has somehow gained infinite lifespans though mutation. I think it's a lot harder to accomplish. I guess a lot of it has to do with degrading DNA (and again, evolution never had to figure out a fix for that because it's a feature not a bug).