“If 60% of people 70-79 become infected and 5.4% die, that’s 3.24% of that group”
If 10% of people 70-79 become infected and 5.4% die, that’s 0.54% of that group
60% is based on the Herd Immunity Threshold for a disease with an R0 of 2.5. Which is what SARS-CoV-2 is.
Your 10% number is based on what, exactly?