From the figures, it looks like 10% of young are still severe pneumonia’s [0]. Not all of those require respirators or ITU, but quite a few will.
The figures depend _hugely_ on the number of sub clinical/mild infections. The UK experts have public ally said they believe the overall mortality rate is at or below 1%. Given a global mortality of ~3% it appears they are assuming two thirds are so mild they didn’t present for testing. You must assume this is based on some evidence not available to the rest of us, or from some simulation based on other findings.