About 50% of the population in that study is over 50. I think it's a bad idea to draw generic conclusions about the disease from a diverse age range. You end up with conclusions that aren't relevant to either. Glossing over the tables I don't see any data about symptomatic over the two weeks by age. I'd be shocked if the rates of becoming symptomatic are not much higher for the elderly and much lower for the young. Didn't read it in depth though.