When I was offered early retirement, I ran all my finances all the way to 100 y.o. Not that I would be expecting to live that long but I wanted to be sure I wouldn't run out of money in my 80s or 90s.
My father had smoked all throughout my childhood and only quit when I left home. He would have been about 53 when he quit. He lived to 85. I believe, at 58 now, I'm way more active than my father was at this age. But in his later years when he gave up driving, he still went out everyday by bus and he was a fairly fast walker.