You first sentence just so convoluted
Yes age and prior health do matter. One is less likely to get sick or may only get slightly ill. Compromised immune system will be most likely to get severely ill. This is true for other illnesses as well
I dont know what youre reading but it has made you irrational.
Age or health does't matter to the 15% or 20% who will go to the hospital. If a 30 year old is in the that percentage it's the same as a 70 year old. They BOTH will go to the hospital. It doesn't matter if that 20% is all 90 year olds. They will go to the hospital. It doesn't matter if they are all 30 year olds. If they're in that percentage they're SICK enough to be in the hospital.