I'm 52 years old and never had the Flu a day in my life.and have never had the flu ,yes, I've had one or two colds, and tummy aches occasionally.
I've got 9 hours of sleep a day, eat a good breakfast, light lunch and a healthy supper(dinner for some) I run a small engine repair shop and do field service and home service, so I'm in contact with the public quite often.
My wife gets the shot every year, and every year she gets the Flu.
I'm not telling others what to do with their immunity, it's just my perspective.