No disrepect, and I'm sure your dad is quite active for his age, but he is still 85 years old. His brain is, his heart and internal organs are, his body is, his eyes and ears are.... He will not be 'fitter than most 60 years olds.' Sorry he just won't be.
I know half a dozen people nearby to me in my village who are 82-87, and they present as quite fit and active. They go for 1 to 1.5 mile walks around the village every other day, go to a hobby group, or do crown green bowling in the village, and do bits of gardening and suchlike, and 3 of them still drive, but no way are they/their health/fitness levels anywhere near as good as mine (I am late 50s/nearly 60...)
My DH is just past 60, and the difference between him (and me) and the people 20-25 years older is very noticeable.
I walk 3-4 miles a day, still work 3 days a week, and think nothing of driving anywhere, anytime, and am strong and fit, and if I fall over/trip, I bounce back up and walk on. Someone of 80+ would need an ambulance if they did that. I don't have hearing aids. Most people I know 80+ absolutely do.... Most have to wear glasses. I don't.
DH is much fitter and stronger than them, he still works 30 hours a week, and he thinks nothing of doing 400-600 mile round trip drives/driving around the mountains in Wales... Or up to Scotland and back... No person I know in their 80s - male or female - will drive that distance. Most of them just pootle up and down to the market town - 10 mile round trip... Occasionally they may go to the nearest big town - 25 mile round trip, but that is rare. They usually go with their adult child who is their 40s or 50s. They will often have one of their adult children take them to hospital appointments too. (Hospital is 40 mile round trip...)
DH and I have both had flu, very bad colds and viruses, food poisoning, and covid over the past few years, and we have bounced back really quickly. Many people 80+ will be hospitalised for weeks... Or will die. (From similar things...)
I'm sure you (and/or someone else) will say your 80+ year old dad or uncle or grandad runs marathons every month, and regularly drives to the South of France and back, and could fall from the top of a flight of stairs/steps and get up and walk off, but in reality, the vast majority will not...
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