First, despite ample opportunity, 83% of the passengers and crew never got the disease. Age didn't make much difference. So, whether it was the isolation after the problem was discovered or a wide spread natural immunity to the virus, most people were spared. Either is good news for us, and dramatically cuts down the severity of our expectations.
Of those who got the disease 48% had no symptoms. Very young were largely spared symptoms. Starting at 20, many more showed symptoms, but it declined as they got older. Even older people had about a 50% of asymptomatic disease. This is bad news for spreading the virus, but good for having it.
Finally, some historical perspective: