No one knows for sure how they will be in their old age. My grandmother didn’t seem to struggle until her mid to late 90s. That’s a lot of years to leave on the table. Years that allowed her to meet and enjoy time with her children, grandchildren, and great-grandchildren.
Had she died at 65, I wouldn’t have even known her. Instead she was around for my entire childhood and well into adulthood.
I'd rather live through my 80s without much struggling. Longevity and quality of life until the end. And I try to live in the way that lends itself towards that.
From what I understand, whether you will struggle depends a lot on whether you eat well, sleep well, drink, smoke, and exercise.
My dad played futsal until the end (~70 yo, car accident, be was perfectly healthy otherwise); I met one of his classmates from school, he looked 20 years older, no exaggeration. My dad looked like he was barely 50.
Note: how old someone looks is very biased by their "generation", as people tend to drink and smoke less these days.
My parents are both 70 and very active. I often meet 65 year olds who are frail and slow with chronic pain and diabetes, when my dad is going on 50 mile bike rides a few times a week. I would hate to develop a significant health condition at 55 and be seriously ill by 60. I would much rather be healthy until my late 70s.
Had she died at 65, I wouldn’t have even known her. Instead she was around for my entire childhood and well into adulthood.