Read the other day that an Italianstudy showed over 99% of the fatalities had a pre-existing condition such as diabetes, asthma etc. Smokers and the obese seem to be considered as having a pre-existing condition. Spanish soccer coach in his 20s: lymphoma. Worth remembering that a good many people have pre-existing conditions they're not aware of. That and just a weak constitution and immune response which some of us are unlucky enough to be born with, probably explains all the younger fatalities.
I'll try to avoid preaching,but an hour's reading online will give a person a good idea what they can do to improve their immune response, at almost any age: diet, hydration (and water quality), exercise, sunlight (Vit. D etc.). Our lymphatic systems only work when we move...
Some context on that here.