Working for the rest of your life may sound unappealing but 100-year-olds around the globe say not retiring is what keeps them feeling youthful and fulfilled.
Not necessarily, as another commenter said they need something "fulfilling" to do with the rest of their lives. After you've been working for 50-60+ years, 5 days a week, 8-16 hours a day, and then you suddenly have every day free you don't know what to do with the time. I've been unemployed a few times for a year at a time and after about 3-4 months it starts to get pretty boring.
My uncle lived to 100, he was completely healthy at 98 and would walk a mile or two a day around town, but broke his hip, the recovery process is practically what killed him because he could no longer be active every day. For like 6-9 months he just sat around, he's muscles and mind atrophied, and the rest of his body started to "fall apart", and he was never the same. He died about a year later.
My brother and I were both worried about our workaholic father when he was about to retire. He made so many projects for himself (genealogy of our family, writing a book, building a mechanical prototype, etc) that he always said he had not enough time in a day.