It's complicated. First of all countries with a relatively young population like South Korea are going to be hit less hard overall than countries with relatively old populations like Italy.
Second, there's going to be a big difference in mortality depending on how the medical system is holding up. In South Korea they got it contained, everybody who needed it got an ICU, and the case fatality rate is less than 1%. In Wuhan they were almost overwhelmed but built some extra hospitals then the they'd been in lockdown longer than the incubation period and they ended up with a bit over a 3% case fatality ratio. In Italy right now the worst hit hospitals are very overwhelmed and performing desperate triage with many infected medical workers and they've got a case fatality ratio over 8%.
Of course, case fatality ratio only covers diagnosed cases. If people with a light fever stay home and don't get tested they won't show up in the denominator and the case fatality ratio will be an exaggeration of the actual fatality ratio. How much of the difference between South Korea and Italy right now is due to which of those factors? I honestly don't know but I am worried. I think mortality rates similar to the Spanish flu could certainly occur if we respond badly enough.
I've not heard any health officials suggest that age is a factor in South Korea's response to the virus. They're only about 3 years younger than Italians [1] -- but have 4x as many hospital beds per capita [2].
It's less about the median age than the numbers in the categories at highest risk. If you compare the population pyramids of the two Italy has many more people over 65. Number of hospital beds per capita is also a big deal.
Second, there's going to be a big difference in mortality depending on how the medical system is holding up. In South Korea they got it contained, everybody who needed it got an ICU, and the case fatality rate is less than 1%. In Wuhan they were almost overwhelmed but built some extra hospitals then the they'd been in lockdown longer than the incubation period and they ended up with a bit over a 3% case fatality ratio. In Italy right now the worst hit hospitals are very overwhelmed and performing desperate triage with many infected medical workers and they've got a case fatality ratio over 8%.
Of course, case fatality ratio only covers diagnosed cases. If people with a light fever stay home and don't get tested they won't show up in the denominator and the case fatality ratio will be an exaggeration of the actual fatality ratio. How much of the difference between South Korea and Italy right now is due to which of those factors? I honestly don't know but I am worried. I think mortality rates similar to the Spanish flu could certainly occur if we respond badly enough.