[mcbits]

I think you're reading it right, assuming they do know the ages of all people hospitalized, and the total cases with known+unknown age have close to the same distribution as the cases with known age. 102 hospitalizations / 1226 total cases = 8.3%.

A huge remaining unknown is how many people were infected but not tested, which would tend to reduce that 8.3% but perhaps not to a negligible level.