Some of it's just luck.
My late husband was very sporty, ran the London Marathon, various road races, did weightlifting, took up karate in his 50s. Suddenly, aged 63, took ill at the dojo where he trained.
It turned out that he had heart trouble. A bit of research showed that it ran in his mother's side of the family. (The men on that side all died in their 60s - uncles, grandfather...) A year later, he had a stent put in. Everything was fine...got his black belt.
Then the signs of angina reappeared. His doctor said that it was his age. Short story: aged 71, he needed open heart surgery. There were complications. He survived, but he was never quite the same. Two years later, he had a stroke which left him with hemiparesis.
My stepdaughter's partner kept himself fit - cycled everywhere. Aged 69, he dropped dead of a heart attack.
My DIL's brother was fifty something when he had a heart attack during a seniors' cycle race. He was resuscitated three times. Survived for a few years with brain damage.
I've known so many people who made it to 60 or 65 and retirement and then suffered from an acute illness just a couple of years later. It's wonderful when people do have a healthy later life, but the years can catch you up.
I'm not dictating that people shouldn't do as they please - I've outlined my experience in a previous post - just suggesting that you should hope for the best but prepare for the worst.
I'm now 65. I'm trying to keep fit but have had various health difficulties caused by my caring duties and the family osteoarthritis has sneaked up on me.