I can't remember the last time I had a cough, cold, sniffle etc. I'm 63, packed up work last year, I spend a lot of time out and about with the two 'Lumps' in my Avatar, mostly on the Seafront as that's where we live. I think doing all the outdoor things and dealing with Pet Care I'm probably exposed to a few more bugs than some others, and build up an immunity of sorts.
My OH is similar age, works 2 or 3 days a week in Local Hospital, nice and warm etc, and doesn't get a lot of fresh air when she's home, apart from The Archers and Emmerdale, and she enjoys a steady stream of minor colds etc.
I'm sure difference in Lifestyle is contributory