The first character that wanted to die was already 105 years old. I guess if you have to look forward to another 100 years, you may just get tired. I think living to maybe 300 years with that kind of tech is enough.. but you never know with people, once they discover they can be immortal, why not ... I guess reality is that there will be something broken and no one can really live 300 years old anymore no matter what kind of medical tech we have except if we "upload" our consciousness into solid state machines.
We often think "If I were in that situation, I wouldn't want to live" but it turns out the survival instinct is strong and even in the case of those who are horribly ill, they often want to stick around to be with their family etc. This whole "seen too much to want to keep living" is romantic sounding and all but I think the truth is, if you didn't want to suicide when you were younger, there's no reason to believe you would want to at 200, 400 etc.