This is typical of coronaviruses, a family that includes the viruses behind the SARS. “Age and your condition in life will really drive your susceptibility. There are two main reasons for older adults’ increased susceptibility to coronaviruses. The first: They are more likely to suffer from underlying conditions that hinder the body's ability to cope with and recover from illness, such as chronic obstructive pulmonary disease.
The second has to do with how our immune response changes with age.