It's definitely a by choice thing. I've gone back to school to learn everything that interests me about Computer Science. I'm 46 years old working on my Bachelors and my goal is to have my PhD and either do research, teach, and write. Or just research and write. Or just write. I'm not sure about that. I do know that I do not EVER want to retire. Everyone I know that has retired by 65 has become bored with life and either an alcoholic or a zombie. I don't ever want to be bored. For me its not even about money. If I'm at least teaching at a community college and making peanuts I don't care. It's about having something to do and instilling a sense of purpose.
I can't remember my history too well but it seems to me that when FDR instituted Medicare & Social Security it was to help our elders so that they wouldn't be in poverty and living on the streets. It was to help them, and possibly educate them, to save for a future without a job. It has become much more then that and a lot of people never really saved their money (or couldn't because they were trying to make ends meet). But everyone I know that has retired seems to have just given up on life and they are bored. Heck, I get bored watching more than two hours of television I can't imagine what I'd do if I didn't have a job or work to do. I don't need the college education though I just want it. I have a good job with a large company that has no problems employing people over 60+ years of age. I can stay here until I'm tired of cube life but I'm ready for a third career and something that is different and fun.
So no I don't ever want to retire. Coming home after a full day of working and simply fading one night when I'm 110 years old just sounds great to me.