I do consider the Diamond Princess to be a valid but rough sample for the ratio of asymptomatic to symptomatic infected - at least as many asymptomatic as symptomatic. IMO that is the only valid virus statistic we can pull from the ship.
Plenty of younger crew. If my memories serve me from my days on cruise ships, there are some middle age range passengers, young couples, some children, even, and a cohort of younger crew to complement the older folks.
I’m not saying it is a perfect representative population, but it isn’t as distorted as you might think.