https://www.imperial.ac.uk/media/imperial-college/medicine/s...
There are 40 million 40-somethings in the USA, you're proposing that 100% of them will have lung damage.
Let's imagine that 80% of the population is infected, that 80% of cases are symptomatic, and that 80% of the 4.90% of hospitalised cases (this 4.90 is direct from the report) get damaged lungs. This is one million 40-somethings, not the entire population.
1 million sounds like a lot, but its only 2.5% of the population at that age range, and assume worst-case.
You know what causes reduced lung functionality in adults? Asthma, driven by air pollution from vehicles and coal power plants. 7.7% of adults have Asthma. Where is the war-scale drive to eliminate fossil-fueled vehicles and power generation?
Vaping. I see most of the young adults doing this. Its probably why they're having the higher hospitalization rates with coronavirus. They already have lung damage.
Might as well just shut the economy down to eliminate that.
It's not just fatalities, hospitalisation i.e. exhausting healthcare facilities is the primary concern with COVID-19.
There is no guarantee that young people wouldn't make up high mortality list in a poor country with high younger population, rich countries should get their acts together to stop that from happening in vulnerable countries.
[1]https://youtu.be/6BOKgSCPD4E?t=32