The death rate for COVID-19 increases significantly at 50+ years of age. It is currently reported as 14.8% for patients 80+ years of age.
https://www.worldometers.info/coronavirus/coronavirus-age-sex-demographics/
It could be due to comorbidities, which dramatically raise the risk of dying from COVID-19 and a sign of declining immunity.
What explains Covid-19’s lethality for the elderly? Scientists look to ‘twilight’ of the immune system