That is very positive. In fact, I am willing to bet there isn't a normal age distribution on the Diamond Princess. It probably lacks a significant under 40 population. Additionally, you don't have a lot of preexisting conditions like in the nursing home in Washington state. The latter is not consistent with the normal population and can be viewed as statistical noise. (not to be insensitive)
That said, being old does not necessarily equate to bad health or even compromised immune systems, just as being young does not equate to a healthy immune system. Two of my grandchildren have asthma, which means they have compromised immune systems. They are about 10 & 6, if I remember correctly. 8>)